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Background: Children in low- and middle-income countries (LMICs) are at risk for problems in cognitive, social and behavioural development. Factors such as a lack of cognitive stimulation and parenting practices that lack sensitivity are central to the genesis of these developmental problems and are exacerbated in the context of poverty. Interventions that target the intersection of early childhood development, parenting, and early violence prevention are required to meaningfully address these problems. One promising intervention for improving parenting and child language and cognitive outcomes is caregiver-child picture book sharing. However, there is a paucity of up-to-date systematic evidence regarding the impact of parent-targeted book-sharing interventions on child and parenting outcomes. In addition, little is known about the mechanisms by which these interventions operate, which include the nature of caregiver-child dialogue. Further, it is unknown whether, in LMIC contexts, certain kinds of caregiver utterances are linked to areas of child development such as social understanding, as has been shown in high-income countries (HIC). Similarly, there is a need to address the shortage of research into how such interventions operate in LMIC settings, where the potential for positive change could arguably be the greatest. A further gap in the literature is the virtual absence of inquiry into the impact of book-sharing interventions on outcomes other than child language. This is surprising, given that such interventions target a set of risk and protective factors implicated in the development of child social understanding and behaviour - such as parental sensitivity, reciprocity, and disciplining strategies. Finally, very little research has looked at moderators that would help to reveal who benefits (or does not benefit) from book-sharing interventions and under what circumstances. Paper 1: The first paper aims to synthesise and appraise existing evidence from randomised controlled trials (RCTs) on the effectiveness of book-sharing interventions on child language and parent book-sharing outcomes. Interventions that train parents to share picture books with children are seen as a strategy for supporting language development. An extensive and sensitive search of seven academic databases was conducted to identify all relevant studies. Screening, extraction and quality ratings were conducted by two independent authors. Meta-analyses were conducted using robust variance estimation modelling on results from 19 RCTs (N= 2,594; child age = 1 - 6 years). Overall, book-sharing interventions had a small sized effect on both expressive language (d=0.41) and receptive language (d=0.26). They had a large effect on caregiver book-sharing competence (d=1.01). The impact of the intervention on child language was moderated by intervention dosage, with lower dosage associated with a minimal impact. Conversely, group-based intervention format was associated with larger impact. Child age and caregiver education level were unrelated to child outcome. This review and meta-analysis demonstrated the promise of book-sharing interventions for enhancing and accelerating child language development and caregiver book-sharing competence, at least in the short term. Paper 2: Social understanding or socio-cognitive development refers to our ability to give psychological explanations for human behaviour and provides the foundation for cooperation and pro-social behaviour. This paper reports a study in which 70 LMIC caregiver-child dyads were assessed to investigate individual and family predictors of child social understanding, with an emphasis on the role of caregiver-child talk. Despite much research into individual and family predictors of socio-cognitive understanding in preschoolers, little is known about corresponding predictors in younger children. Similarly, these relationships are yet to be explored in LMICs. Very little is known about the nature and content of caregiver-child talk in an African context and whether, as has been shown in many HICs, it relates to child social understanding. A better understanding of these relationships could shed light on which elements of caregiver talk could be enhanced in order to aid child socio-cognitive development through an intervention such as book-sharing. For example, this could lay the foundation for addressing the question of whether changes in caregiver talk could in turn lead to improvements in child social understanding. Seventy families with two-year-old children from Khayelitsha, a low-income peri-urban township in South Africa, participated in this cross-sectional study. Two tasks assessing socio-cognitive understanding were administered to the children and video-based transcripts of caregiver-child interactions were coded for mental state talk, causal utterances, and speech quantity. The relationship between caregiver talk and child socio-cognitive development was investigated. Key child and family demographic variables were taken into account. Child language, caregiver education, family socio-economic deprivation, and caregiver references to emotions and causal talk were all associated with child performance on socio-cognitive tasks. After controlling for relevant variables, caregiver causal talk emerged as the most salient predictor of child socio-cognitive performance. This study demonstrated that caregiver talk is associated with child socio-cognitive understanding in a low-income African context. Moreover, it addressed the paucity of research into the nature of this relationship with very young children using measures of fledgling socio-cognitive understanding. The findings suggest that the quality, rather than the quantity, of maternal speech plays an important role in helping children develop socio-cognitive capacities. In particular, speech that involves discussion of causality appears to play a central role. Paper 3: The final paper presents the outcome data from an RCT - the Benefits of Early Book-Sharing study - conducted in Khayelitsha, a low-income peri-urban township in South Africa. The purpose was to evaluate a dialogic book-sharing intervention for caregivers of children 21-28 months, designed to promote positive parenting and child cognitive, socio-emotional, and behavioural development. Families were randomly allocated to a book-sharing or a wait-list control group. In the intervention, caregivers were trained in supportive book-sharing with young children. Training was carried out in small groups over a period of eight weeks. Data were collected at baseline, post-intervention and at six months post-intervention. One-hundred-and-forty caregivers and their 21-28-month-old children (70:70) were assessed at enrolment, with 130 (93%) contributing data at post-intervention and 123 (88%) at a six-month follow-up. Children in the intervention group performed significantly better than controls on a number of observed and caregiver-reported measures of language (d=0.37 - 0.50) and attention (d=0.39 - 0.44). However, few between-group differences were found for observational and caregiver-reported measures of child problem behaviour, pro-social behaviour, and theory of mind. In observed measures, caregivers in the intervention group showed more sensitivity and reciprocity in both book-sharing and free play (d=0.21 - 1.01), and more complex cognitive talk in a narrative task (d=0.65). Further, intervention group dyads engaged in more conversational turns at home (d=0.38), demonstrated through naturalistic measures of the home language environment. Intervention caregivers were also less verbally and psychologically harsh (d=0.19 - 0.43). The Benefits of Early Book-Sharing (BEBS) programme benefitted a number of domains of parenting and child development and holds considerable promise as an early parenting intervention in LMIC contexts. Conclusions: This thesis provides a number of new contributions to the field of early childhood development and parenting in impoverished contexts. A meta-analysis confirmed the promise of book-sharing interventions to improve child language and caregiver book-sharing competence. It also challenged previously held notions that only younger children and more educated caregivers benefit from these interventions. However, it highlighted a gap in the literature regarding effects in LMICs. Further, a detailed investigation into the predictors of child socio-cognitive understanding helped to shed light on the kinds of caregiver language that help to promote their children's socio-cognitive development. The importance of causal talk, in particular, was highlighted. The results from the RCT demonstrated how a book-sharing intervention in a low-income African context could lead to broad improvements in sensitive and reciprocal parenting and improve child language and attention. However, the trial demonstrated limited effects on harsh parenting and child problem behaviour and socio-emotional development, suggesting that more specific and direct programming, possibly within a book-sharing intervention, may be required to address these risk factors.