Durations of less than one second are involved in all kinds of activities, such as music perception or rhythmical production tasks. It is therefore important to know how short durations are processed at a young age. This study aims to define discrimination performance between 3- and 4-year-olds (tempo discrimination). The first 4 years of life are essential for cognitive development and there is little data concerning those years due to the extreme difficulty of finding methods to assess children’s timing performances. Moreover, the results yielded by previous experiments are controversial. Our data revealed that discrimination performances improve significantly within only a few months. The discrimination data from 3 and 4 year-olds are compared to those from older children. The overall results are discussed in a developmental model context.