Over-imitating preschoolers believe unnecessary actions are normative and enforce their performance by a third party.

Over-imitation, which is common in children, is the imitation of elements of an action sequence that are clearly unnecessary for reaching the final goal. A variety of cognitive mechanisms have been proposed to explain this phenomenon. Here, 48 3- and 5-year-olds together with a puppet observed an adult demonstrate instrumental tasks that included an unnecessary action. Failure of the puppet to perform the unnecessary action resulted in spontaneous protest by the majority of the children, with some using normative language. Children also protested in comparison tasks in which the puppet violated convention or instrumental rationality. Protest in response to the puppet's omission of unnecessary action occurred even after the puppet's successful achievement of the goal. This observation is not compatible with the hypothesis that the primary cause of over-imitation is that children believe the unnecessary action causes the goal. There are multiple domains that children may believe determine the unnecessary action's normativity, two being social convention and instrumental rationality. Because the demonstration provides no information about which domains are relevant, children are capable of encoding apparently unnecessary action as normative without information as to which domain determines the unnecessary action's normativity. This study demonstrates an early link between two processes of fundamental importance for human culture: faithful imitation and the adherence to and enforcement of norms.