This paper argues for broader consideration of children's language production systems and, in that context, describes research on children's planning of syntactic structures. The research presented here measures non-fluency patterns in elicited utterances of varied syntactic type. We describe and interpret several regularities in these patterns for two groups of children ("young": three-five-year-olds; and "older": six-eight-year-olds) and an adult comparison group. The evidence indicates a strong correspondence of adult and child responses to structural complexity, both in terms of global fluency measures and in terms of more detailed indicators of planning load. In addition, we report some specific contrasts in the patterning for children and adults that suggest disparities in processing resources and/or in local planning strategies. (Contains 2 figures, 15 tables, and 4 footnotes.)