The purpose of this study was to assess lexical and grammar acquisition in 12 toddlers (age range 24-37 months) who are simultaneously learning Italian and Spanish using information from both languages. A parent semi-structured interview (adapted from Gutierrez-Clellen and Kreiter, 2003) was adopted to assess exposure to each language and to collect other socio-demographic data. The MacArthur Communicative Developmental Inventories, standardized parent report forms in Spanish (Jackson Maldonado et al., 2003) and Italian (Caselli Stefanini and Pasqualetti, 2007), provided measures of expressive vocabulary and grammar in both languages. Data have been codify in order to analyze: i) relationships between children's lexical and grammar repertoire and amount/percentage of input in each language; ii) relationship between lexical repertoire and type of scoring (single language scoring vs. conceptual language scoring, Pearson, Fernandez and Oller, 1993); iii) proportion of different word types in each language considered; iiii) relationship between lexicon and grammar within and between languages. Results indicated that: i) the degree of exposure to each language influenced lexicon and grammar development in that language; ii) the total conceptual language scoring is in bilingual children a better measure of vocabulary size than the single language scoring; iii) proportion of different word types (social words, nouns, verbs and closed class) in each language varied with same-language vocabulary size, except for closed class; iiii) within-language lexicon-grammar associations are stronger than cross-language relationships. Theoretical and clinical implications of these aspects are discussed as contribution in the actual debate about processes underlying bilingual language acquisition and evaluation methods.
