Infants' and young children's perception of the unity of musical events was investigated in three studies. In the first two, children watched video displays of two musicians playing different musical instruments side by side in synchrony, and heard a soundtrack in synchrony with both instruments but specific to one. The children judged which instrument was producing the music they heard. Three- to 4-year-olds differentiated instruments from different families but not instruments from the same family. Five- to 7-year-olds additionally differentiated instrument pairs differing in size and pitch range (e.g., violin, cello). In the third study, infants were presented some of the same musical events in order to assess whether specific experience with the instruments is necessary for perceiving the unity of musical events. Looking times revealed that 7- to 9-month-olds detected the correspondence of the sight and sound of some musical instruments. Specific experience with a variety of instruments is evidently not necessary for detecting correspondences of audible and visible properties and for differentiating instruments from different families.