Michael Tomasello. Becoming Human: A Theory of Ontogeny
—

[ ## Three years old ]

«…age three is a crucial transition point. For most of human evolutionary history, this is the age of weaning, when children start taking their first independent baby steps into the wider world. It is thus at this age that they begin having independent and meaningful interactions with peers, inaugurating what some scholars have dubbed “the two social worlds of childhood”: (1) interactions with knowledgeable and authoritative adults, who provide key experiences relevant to the transmitive dimension of culture; and (2) interactions with coequal peers, who constitute especially challenging partners for social and mental coordination in collaboration and communication, thus providing key experiences relevant to the coordinative dimension of culture. The claim is thus that children before the age of three are mainly adapted for eliciting care and attention from adults, whereas after age three they are prepared for both culturally learning from adult pedagogy as such and developing new skills through coordinative interactions with peers.

[…]

Before age three, children’s executive regulation is mostly individual, as other primates’, although it often works on uniquely human cognitive and social content. After age three, children begin to socially self-monitor their communicative attempts to see if they are comprehensible and rational to others, and they begin to socially self-monitor the impression they are making on others so as to maintain their cooperative identity in the group. In addition, from age three children also collaboratively self-regulate their cooperative interactions with others. Thus, they make joint commitments with others in which “we” make sure that “you” and “I” each behave ourselves, as well as (implicit) collective commitments to the group’s social norms to which “we” make sure that both self and others conform. By engaging in such social and cultural self-regulation from three to six years of age, young children come to create the many and various kinds of self-reflective, normatively structured, and reason-based forms of thought and action that make them for the first time reasonable and responsible persons.»