The ability to learn from expectations is foundational to social and nonsocial learning in children. However, we know little about the brain basis of reward expectation in development. Here, 3- to 4-year-olds (N = 26) were shown a passive associative learning paradigm with dynamic stimuli. Anticipation for reward-related stimuli was measured via the stimulus preceding negativity (SPN). To our knowledge, this is the first study to measure an SPN in children younger than age 6. Our findings reveal distinct anticipatory neural signatures for social versus nonsocial stimuli, consistent with previous research in older children. This study suggests an SPN can be elicited in preschoolers and is larger for social than nonsocial stimuli.