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Sibling relationships appear important in fostering young children's growing theory-of-mind skills, but the quality of sibling interactions has rarely been investigated directly in relation to children's mental-state awareness (e.g. as indexed by talk about perceptions, desires, feelings, cognitions, i.e. inner state talk; IST). This study explored individual differences in young siblings' IST in relation to (i) child characteristics (verbal ability and theory-of-mind task performance); (ii) family characteristics (sib-ship size; social disadvantage, maternal well-being); and (iii) the quality of the children's play with their siblings (frequencies of pretence and reciprocal play). A socially diverse sample of 111 2-year-olds was filmed at home playing with a sib (mean age =4.92 years; SD=1.67 years); these sessions were coded from video for reciprocal play and then transcribed and coded for IST and pretence. Verbal ability was assessed for both sibs; in addition, 2-year-olds completed theory-of-mind tasks. Age and verbal ability were correlated with frequencies of overall talk, IST, pretence and reciprocal play. (Theory-of-mind scores were also correlated with 2-year-olds' IST, but this relation fell below significance once verbal ability was controlled). Significant independent relations were found between IST and children's quality of play, even when age, verbal ability and overall rates of talk were controlled. Although there were no gender contrasts in mean rates or in the variety of IST, gender differences were found in their correlates: in particular, context effects were significantly more important for girls than for boys. Individual differences in children's IST reflect multiple factors, including the dynamic features of children's reciprocal play. [ABSTRACT FROM AUTHOR]

Importance: Although a growing number of studies have reported negative associations of the COVID-19 pandemic with academic performance among school-aged children, less is known about the pandemic's association with early childhood development., Objective: To examine the association between the COVID-19 pandemic and early childhood development., Design, Setting, and Participants: In this cohort study conducted in all accredited nursery centers in a Japanese municipality, baseline surveys of children aged 1 and 3 years (1000 and 922, respectively) were conducted between 2017 and 2019, and participants were followed up for 2 years., Exposure: Children's development was compared at age 3 or 5 years between cohorts that were exposed to the pandemic during the follow-up and a cohort that was not., Main Outcome and Measure: Children's developmental age was measured by nursery teachers using the Kinder Infant Development Scale (KIDS). Data were analyzed between December 8, 2022, and May 6, 2023., Results: A total of 447 children (201 girls [45.0%] and 246 boys [55.0%]) aged 1 year at baseline were followed up to age 3 years, and 440 children (200 girls [45.5%] and 240 boys [54.5%]) aged 3 years at baseline were followed up to age 5 years. During the follow-up, the cohorts that were exposed to the pandemic were 4.39 months behind in development at age 5 compared with the cohort that was not (coefficient, -4.39; 95% credible interval, -7.66 to -1.27). Such a negative association was not observed in development at age 3 years (coefficient, 1.32; 95% credible interval, -0.44 to 3.01). Variations in development were greater during the pandemic than before the pandemic regardless of age. Additionally, the quality of care at nursery centers was positively associated with development at age 3 years during the pandemic (coefficient, 2.01; 95% credible interval, 0.58-3.44), while parental depression appeared to amplify the association between the pandemic and delayed development at age 5 (coefficient of interaction, -2.62; 95% credible interval, -4.80 to -0.49; P = .009)., Conclusions and Relevance: The findings of this study showed an association between exposure to the pandemic and delayed childhood development at age 5 years. Variations in development widened during the pandemic regardless of age. It is important to identify children with developmental delays associated with the pandemic and provide them with support for learning, socialization, physical and mental health, and family support.

This study presents the first quantitative evaluation of the quality of early childhood education and care (ECEC) in Japan to make a significant contribution to the body of knowledge accumulated on ECEC in countries where research has been limited. We observed 30 classes comprising 3-year-olds, 28 classes comprising 5-year-olds, and 30 classes comprising mixed-ages from publicly provided nursery centers under the jurisdiction of the Kanto metropolitan area, Japan. An internationally-recognized quality rating scale for ECEC called the Early Childhood Environment Rating Scale, 3rd edition, which consists of six subscales, was used for this study. In contrast to previous studies conducted in the US, the results of this study showed that the Japanese ECEC is characterized as showing higher scores in the two subscales, "Personal Care Routines" and "Interaction," and showing lower score in the subscale, "Learning Activities." In addition, this study showed that the quality of ECEC varied across nursery centers. Furthermore, with regard to the two subscales, "Interaction" and "Language and Literacy," the degree of variation within centers differed across nursery centers. This study analyzed how these characteristics of Japanese ECEC can be partly produced by the existence of national guideline for nursery centers authorized by the Japanese government. In addition, mechanisms producing differences in the quality of ECEC among and within centers were also discussed., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Fujisawa et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

The Keio Twin Research Center (KoTReC) was established in 2009 at Keio University to combine two longitudinal cohort projects - the Keio Twin Study (KTS) for adolescence and adulthood and the Tokyo Twin Cohort Project (ToTCoP) for infancy and childhood. KoTReC also conducted a two-time panel study of self-control and psychopathology in twin adolescence in 2012 and 2013 and three independent anonymous cross-sectional twin surveys (ToTcross) before 2012 - the ToTCross, the Junior and Senior High School Survey and the High School Survey. This article introduces the recent research designs of KoTReC and its publications.

Identifying the cognitive capacities associated with the development of school readiness is indispensable to support children's successful school transition. It has been shown that executive function (EF) in preschoolers is associated with both concurrent preacademic and subsequent academic skills. However, most research has controlled for the effect of general cognitive ability (GCA), and little research has examined non-English speaking children, which hinders the understanding of the development of school readiness in culturally diverse contexts. In addition, behavioral genetic research on the genetic and environmental influences on this association has been conducted with school-age children. Thus, the genetic and environmental influences on associations between GCA, EF, and preacademic skills during preschool age are unknown. We conducted multivariate behavioral genetic analyses on two waves of longitudinal data at 42 and 60 months of age from 171 and 135 pairs of monozygotic and dizygotic Japanese twins. The findings suggested that a genetic factor influenced GCA at 42 months and mediated preacademic ability at 60 months. In addition, another genetic factor emerged by 60 months that genetically mediated EF and math ability, independent of GCA. Preacademic ability at 60 months was affected by shared environments that influenced EF, rather than GCA, at 42 months. Moreover, shared environments that influenced preacademic ability at 42 months affected later GCA at 60 months. Finally, nonshared environments that had emerged by 60 months mediated these relationships, though the magnitude of this effect was modest. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

This first Japanese twin study of early literacy development investigated the extent to which genetic and environmental factors influence individual differences in prereading skills in 238 pairs of twins at 42 months of age. Twin pairs were individually tested on measures of phonological awareness, kana letter name/sound knowledge, receptive vocabulary, visual perception, nonword repetition, and digit span. Results obtained from univariate behavioral-genetic analyses yielded little evidence for genetic influences, but substantial shared-environmental influences, for all measures. Phenotypic confirmatory factor analysis suggested three correlated factors: phonological awareness, letter name/sound knowledge, and general prereading skills. Multivariate behavioral genetic analyses confirmed relatively small genetic and substantial shared environmental influences on the factors. The correlations among the three factors were mostly attributable to shared environment. Thus, shared environmental influences play an important role in the early reading development of Japanese children.

This twin study examined the bidirectional relationship between maternal parenting behaviors and children's peer problems that were not confounded by genetic and family environmental factors. Mothers of 259 monozygotic twin pairs reported parenting behaviors and peer problems when twins were 42 and 48 months. Path analyses on monozygotic twin difference scores revealed that authoritative parenting (the presence of consistent discipline and lack of harsh parenting) and peer problems simultaneously influenced each other. Authoritative parenting reduced peer problems, and peer problems increased authoritative parenting. Neither consistent discipline nor harsh parenting alone was associated with peer problems. These results suggest that maternal authoritative parenting works protectively in regard to children's peer problems, and peer problems can evoke such effective parenting., (© 2012 Blackwell Publishing Ltd.)

This study examined the link between sibling relationships and children's social adjustment by comparing twin siblings and siblings with different ages (singleton siblings}, and clarified the role of reciprocity in sibling relationships on children's social development. Mothers of 58 monozygotic twin pairs, 48 dizygotic twin pairs, and 86 singleton sibling pairs reported their children's sibling relationships and social adjustment.This study showed that the effects of sibling relationships on the prosocial behaviors and conduct problems of each child are stronger for twins than for singleton siblings. Moreover, positivity toward one's sibling increased peer problems only among monozygotic twins. The opposite tendency was present among dizygotic twins and singleton siblings. This study suggests the importance for children's social development of having many interactions with siblings and establishing reciprocity in sibling relationships. Moreover, our results suggest that the quality of sibling relationships among monozygotic twins may be different from those among dizygotic twins and singleton siblings.

This study investigated the association between negative parenting (NP) and conduct problems (CP) in 6-year-old twins, taking into account the severity of hyperactivity/inattention problems (HIAP). Analyses of the data from 1,677 pairs of twins and their parents revealed that the shared environmental covariance between NP and CP was moderated by the level of HIAP but not by CP or NP, where the shared environmental covariance was larger in children with higher levels of HIAP than in children with lower levels of HIAP. The genetic covariance between NP and CP was not moderated by the level of HIAP, whereas it was larger in the group with lower levels of CP and NP than in the group with higher levels. These results suggest that severe HIAP strengthens shared environmental associations between NP and CP and that interventions focusing on the shared environmental component of NP would be effective for parents and children with severe HIAP.

Although growth in head circumference (HC) during infancy is known to predict later childhood outcomes, the mechanisms underlying this association with later sociocognitive abilities remain undetermined. Thus, using a sample of 241 pairs of normally developing Japanese twins, this study investigated the underpinnings of the association between HC growth (difference between HC at birth and at 10 months) and sociocognitive abilities at 19 months as measured by 10 items from the M-CHAT. Phenotypic correlations between HC at birth and sociocognitive abilities and between HC growth and sociocognitive abilities were marginal and not significant. However, multivariate genetic analyses using Cholesky decomposition revealed that genetic influences on HC growth and those on sociocognitive abilities were negatively associated. On the other hand, shared and nonshared environmental influences on HC growth were positively associated with influences on sociocognitive abilities. Genetic and environmental influences on HC at birth were not significantly associated with influences on sociocognitive abilities. These results help to clarify the role of brain growth during infancy in the subsequent development of sociocognitive abilities and highlight the importance of examining the different roles of genetic and environmental influences in studies of these areas., (© 2011 Blackwell Publishing Ltd.)

The Tokyo Twin Cohort Project (ToTCoP) is a large-scale longitudinal study of 5 years based on 1619 pairs of infant twins reared together. The purpose of the study is to construct a population-based twin registry in Japan and to investigate human growth and development and twin themselves. It covers behavioral, neurological, physical and environmental variables measured by questionnaire, home visiting and brain imaging technology. The full registry contains over 47,000 multiple births collected from the Basic Resident Register, and the targeted population is 3070 probable twins of 0 to 2 years old. Preliminary analysis of the entry questionnaire data showed no serious sampling biases. Descriptive statistics of parental characteristics (parental age, gestation age, parity and placentation, maternal weight, parenting stress) and children's characteristics (body size at birth, 4 and 10 months of age, milk consumption, and sleeping and social behavior) and their correlations, genetic and environmental contributions and correlations are reported.

This article reports developmental changes relating to reconciliation and bystanders' affiliation with victims of aggression (i.e., consolation) among 3- to 5-year-old Japanese preschool children. Use of the post-conflict-matched control (PC-MC) method revealed that the frequency with which reconciliation and consolation were offered to a victim increased steeply in 5-year-olds, compared with 3- and 4-year-olds. The complexity of contextual factors affecting the occurrence of reconciliation and the form of consolation increased with age. Consolation occurred more often before reconciliation than after among all but the 3-year-olds and occurred more often when no reconciliation occurred than when it did occur among all classes. These findings support the view that consolation functions as a substitute for reconciliation, lessening the tension experienced by the victim of aggression., (((c) 2006 APA, all rights reserved).)