Gender segregation describes the general tendency for children to prefer interactions with same-sex peers as opposed to peers of the opposite gender. This preference is observed early in young toddlers and peaks around 8-11 years of age.
Gender segregation has been shown to be cross-cultural and is even evident is some non-human primates. The separation of genders in play is typically initiated by children themselves with girls tending to play with girls and boys preferring to play with boys. Gender segregation typically begins to wane by adolescence.