Researchers of child language have typically assumed that the acquisition of grammatical morphemes provides evidence of syntactic competence. However, experimental research by Gerken (1996) and colleagues suggests that the variable appearance of some grammatical morphemes may be conditioned by phonological factors. This talk reviews some of our recent corpus research on English and French, showing that 2-year-olds are much more likely to produce grammatical morphemes such as determiners and 3rd person singular -s in prosodically ‘unmarked’ contexts. These findings suggest that some of the language-internal and crosslinguistic variability found in morpheme production is systematic and predictable. This suggests that young language learners may exhibit earlier syntactic competence that typically assumed.