The central claim in Amaral and Roeper's (this issue; henceforth A&R) keynote article is that everyone is multilingual, whether they speak one or more languages. In a nutshell, the idea is that each speaker has multiple grammars or "sub-sets of rules (or sub-grammars) that co-exist". Thus, rather than positing complex rules to account for the intricacies of a given linguistic property, e.g. residual V2 in English, the theory of Multiple Grammars (MG) posits that speakers have several simpler rules which operate in parallel, something which the authors argue is more in keeping with minimalist grammar. The source of these multiple grammars is contradictory information in the input to the language-learning child. Even in monolingual societies, the authors claim, children are regularly provided with conflicting input as a result of, for example, language change and lexical exceptions to (morphosyntactic) rules. After developing multiple grammars to cope with this, children then use "linguistic cues to figure out which of [their] sub-grammars are dominant and productive, and which ones are lexically motivated and idiosyncratic". In the keynote article, A&R turn to (adult) second language (L2) acquisition, claiming that multiple grammars are "the primary source for optionality in all stages of adult L2 acquisition". This commentary considers how MG can be applied to bilingual language development in early childhood, and the extent to which this proposal aligns with the data available from bilingual children. Bilingual acquisition presents an interesting test case for MG because, as in adult L2 acquisition, it entails more than one language and, as in L1 acquisition, it involves considerable -- and probably more -- variation. The focus of this commentary is on the hypothesis that multiple grammars derive from contradictory information in the input, and it explores the extent to which this and the wider proposal of MG can be applied to bilingual children.