This paper introduces a model being developed for estimating child and adolescent formant frequency values from adult data. The model approximates adult male and female pharyngeal and oral cavity lengths, and scales these along the corresponding male or female growth curve. The second and third formant frequencies are estimated directly from these scaled vocal tract dimensions. Two methods of establishing the first formant from the scaled data are discussed. Initial results obtained in the scaling of adult data to child values suggest that age, height and gender are all significant when estimating child formant frequency values. Furthermore, averaging of male and female data is found to be inappropriate since the differing growth rates of males and females imply that vocal tract dimensions cannot be linearly related.