The development of prosodic capabilities in infants has been studied extensively. Results have, however, often been contradictory, in part because approaches to the study have been divergent. A traditional approach with an innatist bias has sought to demonstrate very early mastery of adult-like speech characteristics of the prosodic system. More recently, research has sought to illustrate that infants actively build a phonological system, including both prosodic and syllabic features. In our approach, adult-like features of speech are not expected to emerge fully formed early in life, but to unfold in infrastructural stages. We preview a longitudinal project on infant vocal development, and argue that two widely-studied prosodic phenomena (final-syllable lengthening and pitch control) show complexities that require recognition of the infants active participation in development of prosody. This exploratory participation leads to nuances that contradict simplistic generalizations about early emergence of adult-like prosodic structures.