Social play begins early with smiling and cooing, imitation and peek a boo. Children then learn to share toys during play with others and they continue to develop social skills that involve turn taking and following the rules. As children grow and develop their play moves from solitary to parallel play (where children play alongside but not with each other) then onto social play (where children share and interact directly).
For young people a significant amount of the leisure time involves spending time with friends in activities they enjoy doing together. They might not perceive this as 'play' however it is still classed as social interaction.