The goal of this article is to examine the factors that are proposed in the literature to explain the success--failure in the child L2 (second language) acquisition of grammatical gender in Dutch definite determiners. Focusing on four different groups of bilingual children, we discuss four external success factors put forward in the literature: (1) early age of onset, (2) lengthy and intensive input, (3) the quality of the input and (4) the role of the other language. We argue that the first two factors may indeed contribute to explaining the differences in success between the less and more successful bilingual children. However, the influence of the quality of the input in (standard) Dutch appears to be inconclusive, whereas the (structural) similarity of the gender systems in the two languages may reinforce the children's awareness of the grammatical gender category. Moreover, it appears that individual bilingualism vs. societal bilingualism, that is the sociolinguistic context in which Dutch is acquired, is not a factor for failure or success with respect to the acquisition of grammatical gender. In the final part of this article, we hypothesize that the important role of the input is related to a language internal factor, which distinguishes the Dutch gender system of the definite determiner from that of other languages, resulting in different acquisition paths. (Contains 4 tables and 15 footnotes.)