To perform everyday tasks, such as crossing a road, we greatly rely on our sight. However, certain situations (e.g. an extremely dark environment) as well as visual impairments can either reduce the reliability of or completely remove this sensory information. In these cases, the use of other information is vital. Here we seek to examine the development of haptic and auditory integration. Three different groups of adults and 5- to 12-year-old children were asked to judge which of a standard sized and a variably sized ball was the largest. One group performed the task with auditory information only, haptic only or both. Auditory information about object size came from the loudness of a naturalistic sound played when observers knocked the ball against a touch-pad. A second group performed the same conditions, while wearing a thick glove to reduce the reliability of the haptic information. Finally, a third group performed the task with either congruent or incongruent information. Psychometric functions were fitted to responses in order to measure observers’ sensitivities to object size under these different conditions. Integration of haptic and auditory information predicts greater sensitivity in the bimodal condition than in either single-modality condition. Initial results show that young children do not integrate information from haptic and auditory modalities, with some children aged below 8 years performing worse in the bimodal condition than in the auditory-only condition. Older children and adults seem able to integrate auditory and haptic information, especially when the reliability of the haptic information is reduced.