A central concern of scholars of bilingualism is the extent and causes of phenomena that seemingly result from the close contact of two (or more) grammatical systems. Societal bilingualism is characterized by constant and rapid changes which may be observed as they arise and spread in the linguistic and social systems. Likewise, bilingual first language acquisition is characterized by constant changes as children become cognitively and linguistically more mature. This article compares aspects of the grammars of two developing English-Spanish bilinguals with those of adult bilinguals in order to examine the general issue of intergenerational continuity and change in a situation of societal bilingualism. Two types of contact-induced change are identified: copy, a qualitative mechanism that underlies the notion of transfer, and quantitative influence, that is, patterns that are frequent in one language affect the frequency of parallel patterns in a contact language. Changes caused by copying are clearly the result of contact, while those that result from influence may have an internal or an external motivation, or both. The study supports the hypothesis that crosslinguistic interaction affects the lexicon and discourse-pragmatics, but not the core syntax of the languages. Some concrete connections are indentified between early bilingual grammars and those of adult bilinguals, namely the increased production of overt subject pronouns and preverbal subjects,a reduced verbal system, and the reproduction of the meaning of word combinations from English into Spanish. The theoretical implications of the parallels identified between the children’s linguistic behavior and that of adult bilinguals are discussed.