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Purpose: The goal of this work was to examine the semantic and syntactic properties of the vocabularies of autistic and non-autistic infants and toddlers to see if children in these two groups know different kinds of words. We focused on both receptive and expressive vocabularies. For expressive vocabulary, we looked only at the “active” lexicon: Of those words that are already in children's receptive vocabulary, we asked which ones they also produce. Method: We used an existing data set of 346 parent report vocabulary checklists (MacArthur–Bates Communicative Development Inventory: Words and Gestures) from 41 autistic and 27 non-autistic children at multiple timepoints between the ages of 6 and 43 months. We coded the words on the checklists for various semantic and syntactic properties and evaluated which properties predicted whether children understood and produced those words. Results: Overall, we replicated a common finding that autistic children have smaller receptive vocabularies than non-autistic children, but we found that of the words they understand, autistic children produce a similar proportion of those words as non-autistic children. While we found that some syntactic properties are more or less likely to be represented in children's early vocabularies (e.g., nouns are more likely to be understood and produced than words that are not nouns), these patterns did not differ across autistic and non-autistic children. Conclusions: The semantic and syntactic compositions of autistic and non-autistic children's vocabularies are similar. Thus, while receptive vocabularies are relatively smaller for autistic children, they do not appear to have specific difficulty with words that have particular syntactic or semantic properties, or with adding words to the expressive vocabulary that they already understand.

Parents are the first to indicate concerns about their child’s development in up to 80% of children with autism spectrum disorder (ASD). They often notice symptoms related to ASD around the first two years, but the average age of diagnosis is 3.5 years old. This study examined the relationships between parents’ early concerns and the time lag between suspicion and diagnosis. Forty-eight Spanish-speaking families were enrolled in this study. Parents were asked about early signs that made them think that their child could possibly have ASD. Mediation analyses showed that the child’s age at suspicion mediated between sibling status and the time lag between suspicion and a formal diagnosis (β = –.53,p< .01). Having another child with typical development accelerated parents’ detection of ASD signs (β = –.62,p< .001). The number of social-communication concerns that parents detected mediated this relationship (β = –.28,p< .01). Parents who reported more social-communication concerns perceived these signs earlier, but have to cope with a longer time lag until diagnosis than those who reported more concerns related to restrictive and repetitive behaviors and interests, or other developmental concerns. Moreover, this relationship between concerns of ASD and the diagnoses was explained by the child’s age. Training pediatricians on how to respond to parent questions and concerns could reduce the time lag between parents’ concerns and diagnosis of ASD.