Children's early word productions often differ from the target form, sometimes exhibiting vowel lengthening when word-final coda consonants are omitted (e.g., dog /d g/ → [d :]). It has typically been assumed that such lengthening compensates for a missing prosodic unit (a mora). However, this study raises the alternative hypothesis that vowel lengthening in early productions compensates for the missing coda segment. If lengthening selectively occurs with short/lax vowels but not long/tense vowels, this would provide support for the hypothesis that lengthening serves to preserve bimoraic or `minimal word' structure. However, if lengthening occurs across the board, this would indicate that lengthening compensates for the omitted segment. In order to address this issue, matched word pairs produced with and without a coda were extracted from the spontaneous speech of three English-speaking children between the ages of 1;1 and 2;6. Phonetic analysis compared the duration of vowels in words with and without the coda. The results showed that two children lengthened both short and long vowels when the coda was omitted, whereas one child selectively lengthened only short vowels. The implications of these findings, both for the representation of prosodic words, and for theories of production more generally, are discussed.