Cross-linguistic similarities and differences in early lexical and grammati
cal development are reported for IOOI English-speaking children and 386 Ita
lian-speaking children between 1;6 and 2;6. Parents completed the English o
r Italian versions of the MacArthur Communicative Development Inventory: Wo
rds and Sentences, a parent report instrument that provides information abo
ut vocabulary size, vocabulary composition and grammatical complexity acros
s this age range. The onset and subsequent growth of nouns, predicates, fun
ction words and social terms proved to be quite similar in both languages.
No support was found for the prediction that verbs would emerge earlier in
Italian, although Italians did produce a higher proportion of social terms,
and there were small but intriguing differences in the shape of the growth
curve for grammatical function words. A strikingly similar nonlinear relat
ionship between grammatical complexity and vocabulary size was observed in
both languages, and examination of the order in which function words are ac
quired also yielded more similarities than differences. However, a comparis
on of the longest sentences reported for a subset of children demonstrates
large cross-linguistic differences in the amount of morphology that has bee
n acquired in children matched for vocabulary size. Discussion revolves aro
und the interplay between language-specific variations in the input to youn
g children, and universal cognitive and social constraints on language deve
lopment.