Parents of 592 children between the age of 0 ; 8 and 1 ; 4 completed the Estonian adaptation of the MacArthur-Bates Communicative Development Inventory (ECDI Infant Form). The relationships between comprehension and production of different categories of words and gestures were examined. According to the results of regression modelling the production of object gestures and gestural routines was positively correlated with the use of all the word categories. Comprehension of common nouns was positively correlated to the production of common nouns and predicates, whereas the comprehension of predicates was negatively correlated to the production of common nouns and social terms. The older the children were the more they produced words from each category. Girls were reported to produce more social terms. First-born children had an advantage over later-born children in the production of common nouns. Maternal educational level was associated with the production of common nouns and predicates.

Parental reports are a widely-used source of information about infants’ and toddlers’ communicative skills, but parent-report instruments valid for children older than 30 months are less known. This study explored individual variability in children’s communicative skills at the age of 3;0 via parental reports using the Estonian (E) CDI-III. The validity of ECDI-III was established through correlations with another parent-report instrument (ECDI-II) and a standardized examiner-administered language assessment (New Reynell Developmental Language Scales; NRDLS). A hundred Estonian-speaking children ( M age = 35.77 months, age range from 34 to 39 months; 20 of them with reported language difficulties) participated in the study. Relations between different communicative skills and the impact of such factors as the child’s gender, maternal and paternal education, reported language difficulties, the number of siblings, and day care attendance on variability in vocabulary size were also considered. The results showed that the ECDI-III components were moderately to strongly associated with each other, with the ECDI-II and NRDLS. Children with reported language difficulties scored lower on all language measures, except for orthographic awareness. Girls, children of more educated mothers, children with older siblings, and those who had attended day care for more months obtained higher vocabulary scores.

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Cross-linguistic studies can provide information about general and language specific features of language development, but relatively few such studies are available in the literature. The main aim of the present study was to investigate, from a cross-linguistic perspective, the roles of the internal factor of gender and the external factors of birth order and parental education level on development of language in 2-year-old children. We examined 351 children growing up in the three European language contexts of Croatian (N=104), Estonian (N=141) and Finnish (N=106).Information on lexical skills and word combination ability was collected using the short form of the MacArthur-Bates Communicative Development Inventories, and the influence of background factors on these aspects of language development was investigated. No significant differences were found in lexical skills or word combination ability among the three language groups. These aspects of language development varied significantly with gender, but not with the external factors. Our findings suggest that internal factors may influence early language development more than external factors.

The growth rate and the composition of expressive lexicon was studied in a sample of 903 infants between the age of 0;8 and 1;4 whose parents completed the Estonian adaptation of the MacArthur–Bates Communicative Development Inventory – Words and Gestures. As expected, older children had on average larger vocabularies compared to younger children. At the age of 1;4 the Estonian infants’ lexicon was smaller compared to the American-English children’s lexicon but larger than Italian and British-English infants’ vocabularies. The Estonian infants’ expressive lexicon has the same proportional distribution of semantic categories that other languages have been shown to have. On average, Estonian girls have larger vocabularies compared to boys. There are also some differences between boys and girls regarding the content of most frequently produced words. Results provide additional information about the rate of lexicon learning and proportional distribution of semantic categories in a language with rich morphology.