According to Crain and Nakayama (1987), when forming complex yes/no questions, children do not make errors such as Is the boy who smoking is crazy? because they have innate knowledge of structure dependence and so will not move the auxiliary from the relative clause. However, simple recurrent networks are also able to avoid such errors, on the basis of surface distributional properties of the input (Lewis & Elman, 2001; Reali & Christiansen, 2005). Two new elicited production studies revealed that (a) children occasionally produce structure-dependence errors and (b) the pattern of children's auxiliary-doubling errors (Is the boy who is smoking is crazy?) suggests a sensitivity to surface co-occurrence patterns in the input. This article concludes that current data do not provide any support for the claim that structure dependence is an innate constraint, and that it is possible that children form a structure-dependent grammar on the basis of exposure to input that exhibits this property.