According to research presented by Robin Banerjee of Sussex University, there is pressure on boys to be boys from as young as four.
In a survey of 64 four to nine-year-olds in Brighton schools, Mr Banerjee asked children on their own and then in a group of same-sex peers to describe themselves and what they played with. Boys said they were more masculine with their peers than when alone.
Girls did not seem to be influenced by the presence of same-sex peers. Mr Banerjee said: "Boys are seeking approval from their peers right from the beginning of primary school."