Research into the developing vowel system has assumed greater importance in recent years with growing evidence for a more important theoretical role for vowels in child phonology. One limitation of acoustic studies in child speech has been the practical difficulties associated with formant-based analysis and the experiments reported in this paper compare the reliability of critical bands and formant frequencies as acoustic correlates of vowel identity in children. Gaussian classification of vowels in/CVd/Australian English words was carried out using data collected from 4-year-old children and male and female adults. The results show that the use of critical bands for the classification of vowels in children is a robust technique which requires less experimenter intervention in the analysis procedure than the use of formant frequencies, while achieving similar results. The ability to utilize an automatic methodology such as critical band analysis can provide a very powerful tool for large-scale studies in this area.