Do children use the same properties as adults in determining whether music sounds happy or sad? We addressed this question with a set of 32 excerpts (16 happy and 16 sad) taken from pre-existing music. The tempo (i.e. the number of beats per minute) and the mode (i.e. the specific subset of pitches used to write a given musical excerpt) of these excerpts were modified independently and jointly in order to measure their effects on happy-sad judgments. Adults and children from 3 to 8 years old were required to judge whether the excerpts were happy or sad. The results show that as adults, 6--8-year-old children are affected by mode and tempo manipulations. In contrast, 5-year-olds' responses are only affected by a change of tempo. The youngest children (3--4-year-olds) failed to distinguish the happy from the sad tone of the music above chance. The results indicate that tempo is mastered earlier than mode to infer the emotional tone conveyed by music.