Previous studies have suggested that intonation development in infants and toddlers reflects an interaction between physiological and linguistic influences. The immediate background research for this study, however, was based on vocalizations that were only one syllable in length. By extending the analysis to polysyllabic utterances, the present study evaluated a broader range of physiological constraints on intonation production than the maximally simple context of monosyllabic utterances had permitted. The width and direction of pitch change across one- and two-syllable nuclear tones were acoustically analyzed in utterances produced by 60 children between the ages of 0;6 and 1;11. The results showed that the children controlled the characteristic intonation pattern of English monosyllables by the age of 1;6-1;8. However, even the youngest groups of children produced relatively robust and adult-like intonation contours when the tone-bearing string was polysyllabic, suggesting that the trochaic or dactylic foot is the natural 'unmarked' unit of tone production. The asymmetrical results for one- versus two-syllable tones support the conclusion that width of pitch change largely reflects physiological universals in children's earliest vocalizations and language-specific learning after the age of 1;6. Implications of the findings are also discussed in relation to the Trochaic Template Hypothesis. It is concluded that a bias for trochaic rhythms that some children demonstrate could be based, in part, on the child's sensitivity to physiological constraints on the velocity and range of intonational pitch change.