This article reexamines Critical Period and L1/L2 differences by looking at the development of Spanish morphosyntax by young Anglophone immersion learners, in light of two hypotheses, Full Transfer/Full Access (FTFA) and Failed Functional Features (FFFH). FTFA maintains that syntax and morphology develop separately in L2 acquisition for adults and children, while FFFH holds that syntax is dependent on morphology development and that a post-Critical Period failure of morphosyntactic functional features contributes to an L1A/ adult L2A distinction. We first review L1A and L2A of Spanish morphosyntax and elaborate FFFH and FTFA. Then we describe our data collection, results and discussion in terms of the two hypotheses.We conclude that the child learners are sensitive to the importance of inflectional morphology (L1A-like), but make numerous errors (adult L2A-like). Their syntax develops more quickly and accurately than their morphology, supporting FTFA.