We live in a multisensory world and one of the challenges the brain is faced with is deciding what information belongs together. Our ability to make assumptions about the relatedness of multisensory stimuli is partly based on their temporal and spatial relationships. Stimuli that are proximal in time and space are likely to be bound together by the brain and ascribed to a common external event. Using this framework we can describe multisensory processes in the context of spatial and temporal filters or windows that compute the probability of the relatedness of stimuli. Whereas numerous studies have examined the characteristics of these multisensory filters in adults and discrepancies in window size have been reported between infants and adults, virtually nothing is known about multisensory temporal processing in childhood. To examine this, we compared the ability of 10 and 11 year olds and adults to detect audiovisual temporal asynchrony. Findings revealed striking and asymmetric age-related differences. Whereas children were able to identify asynchrony as readily as adults when visual stimuli preceded auditory cues, significant group differences were identified at moderately long stimulus onset asynchronies (150–350 ms) where the auditory stimulus was first. Results suggest that changes in audiovisual temporal perception extend beyond the first decade of life. In addition to furthering our understanding of basic multisensory developmental processes, these findings have implications on disorders (e.g., autism, dyslexia) in which emerging evidence suggests alterations in multisensory temporal function.