Recent advances in linguistic theory within the principles and parameters framework have exerted considerable influence on the field of second language acquisition. SLA researchers working within this framework of syntactic theory have investigated the extent to which developing second language grammars are constrained by principles of Universal Grammar (UG). Much of the UG-based SLA research in the 1980s focused on adult L2 acquisition, but the role of UG principles in child L2 acquisition remained largely unexplored. More recently, however, this state of affairs has begun to change as SLA researchers are becoming more and more interested in child second language syntactic development. In this paper, I review recent and current developments in UG-based child SLA research, and I argue that child SLA has a valuable role to play in enabling us to arrive at a better understanding of the role of biological factors in language acquisition and in strengthening the links between SLA and linguistic theory. Specifically, I discuss the findings of child SLA studies with respect to the following issues: the role of UG parameters in child SLA, the status of functional categories and their projections in child SLA, and the nature of the evidence available to and used by child L2 learners. The overall picture emerging from these studies suggests that child L2 developing grammars are indeed constrained by Universal Grammar. While it is not fully clear at the present time whether the child L2 learners& knowledge is a result of direct access to UG or indirect access to UG (i.e., through the mediation of the L1), the evidence indicates that L1 transfer (at least in certain syntactic domains) cannot be entirely ruled out.