We conducted two naturalistic experiments to investigate preschoolers’ development of event-based prospective memory (PM) and to examine the effects of motivation and interruption of an ongoing task. Children aged 2-6 years were asked to perform familiar PM tasks while engaged in their habitual kindergarten play. PM performance improved systematically across the preschool years. The type of PM response (motor or verbal) did not affect performance. High motivation was necessary for 2-year-olds to perform well, and it remained an important factor that increased performance across the entire preschool age range. The need to interrupt an ongoing activity decreased performance in 3-, 4-, and 5-year-olds, but not in children aged 2 or 6 years. The pattern of results is consistent with explanations for interruption effects that highlight the role of inhibitory control.