Spontaneous speech samples were collected from 40 Cantonese-speaking children aged between 10 and 27 months. Over 7,000 vowels and diphthongs were transcribed and analysed to determine the accuracy of production of Cantonese vowels and diphthongs. A model of feature complexity was derived from the distinctive features of vowels to predict the route of development of vowels and diphthongs. Two factors were found to affect development: a linguistic factor (frequency of occurrence in the ambient language) and an articulatory factor (feature complexity). Early dependence on the feature complexity of segments at 15-18 months is superseded by ambient language influences by 24 months of age.