High-pitched productions present difficulties in formant frequency analysis due to wide harmonic spacing and poorly defined formants. As a consequence, there is little reliable data regarding children’s spoken or sung vowel formants. In order to circumvent the problem of wide harmonic spacing, 29 11-year-old Swedish children were asked to produce four sustained spoken and sung vowels with a sweeping F0. F1 and F2 measurements were taken. Experienced choir singers were used as subjects in order to minimise the larynx height adjustments associated with pitch variation in less-skilled subjects. Results showed significantly higher formant frequencies for speech than for singing. Formants were consistently higher in females than in males suggesting longer vocal tracts in these preadolescent boys. Furthermore, formant scaling demonstrated vowel-dependent differences between boys and girls suggesting non-uniform differences in male and female vocal tract dimensions. These vowel-dependent sex differences were not consistent with adult data.