Overimitation represents an early developing behavior implicated in the emergence of learning, affective, and social competences. Adult overimitation is heavily affected by contextual variables such as social ostracism, the experience of being ignored by others in a social context, an experience that threatens several psychological needs, inducing the urge to reaffiliate with a social group to restore the original state of well-being. Yet, the impact of social ostracism on overimitation in children remains unclear. This study explored how a face-to-face triadic inclusive/ostracizing ball-tossing game affects overimitation in predominantly White 3-year-old children (n = 43, 53.4% boys) and 5-year-old children (n = 43, 41.8% boys). Results showed that preschoolers are highly affected by social ostracism experiences, with both age groups displaying decreased positive emotionality and heightened negative emotionality when ostracized. Despite this continuity in the affective and behavioral reactions toward social exclusion, imitation fidelity is differently affected by first-person ostracism; the 3-year-olds imitated more when ostracized, whereas the 5-year-olds did so when included, signaling a developmental difference between the strategy repertoire at different ages. Overall, the current findings shed light on the social influences driving preschoolers’ overimitation behaviors, emphasizing the importance of investigating social mechanisms underlying imitation and young children’s social cognition development.