Researchers have long been puzzled by children's variable omission of grammatical morphemes, often attributing this to a lack of semantic or syntactic competence. Recent studies suggest that some of this variability may be due to phonological constraints. This paper explored this issue further by conducting a longitudinal study of five English-speaking one- to two-year-olds' acquisition of articles. It found that most children were more likely to produce articles when these could be produced as part of a disyllabic foot. However, acoustic analysis revealed that one child initially produced all articles as independent prosodic words. These findings confirm that some of the variable production of articles is conditioned by constraints on children's early phonologies, providing further support for the Prosodic Licensing Hypothesis. They also hold important implications for our understanding of the emergence of syntactic knowledge.