Recursive NPs are difficult to produce and late to emerge. We compare prosodic and syntactic abilities in Japanese-speaking five- and six-year-olds (n = 28) and adults (n = 10). It is reported that syntactic structure in Japanese is prosodically marked via downstep and metrical boost. Results of an elicited imitation task suggested that children had acquired the lexical prosody (contrast between accented and unaccented words), a pre-requisite for downstep realization. While downstep, the prosodic phrasing involved in the complex NPs in this study, was established, children showed interspeaker variation with the metrical boost, a feature that distinguishes recursively embedded NPs from non-recursive NPs. However, variability was also found in adults, indicating that, in contrast to previous results, prosodic encoding of syntax is generally unreliable in adult speech. Finally, the magnitude of metrical boost was not correlated to children's ability to produce recursive possessives, suggesting that prosody does not help bootstrap Japanese children's recursive phrases.