Book excerpt: This volume presents recent generative research on the nature of grammars of child second language (L2) acquirers -- a learner population whose exposure to an L2 occurs between the ages of 4 to 8. The main goal is to define child L2 acquisition in relation to other types of acquisition such as child monolingual and bilingual acquisition, adult L2 acquisition, and specific language impairment. This comparative perspective opens up new angles for the discussion of currently debated issues such as the role of Universal Grammar in constraining development, developmental sequences in L2, maturational influences on the 'growth' of grammar, critical period effects for different linguistic domains, initial state and ultimate attainment in relation to length of exposure, and L1-transfer in relation to age of onset. These issues are explored using longitudinal, cross-sectional, and experimental data from L2 children acquiring a range of languages, including Dutch, English, French, and Greek.