Age 2. Children first begin to play together, rather than alone

Age 3. Pro-social beahviour – helping other children and sharing – begins. At this time fights are also common as they learn how to share

Age 4. Friendships grow stronger as they start school and spend more time away from the family

Age 7. Self-identity is tested and children choose friends with common interests. Boys and girls tend to separate, with girls forming more itimate friendships, often pairing up as 'best friends'

Age 10. As children share more personal information with each other, friendships deepen. Girls especially can find themselves vulnerable to the social minefield of gossip and exclusion at times, which begins to take shape in the playground

Age 13 upwards. Friendships now become more like adults' friendships, but can be more intense as peers are far more central to teenage identiy than family relationships. More cross-gender friendships appear now too