There are some child friendly social media sites that are suitable for kids of all ages.
Disney's Club Penguin is one of the most popular sites, with over 28 million users worldwide. It allows kids to make their own penguin 'avatar', make friends with other penguins, play games and take part in lots of other activities. It's free to join and designed for kids 6 and up.
Poptropica is a virtual online world in which kids can customise an online character to travel across the world, meeting other kids and playing games along the way. It is has one of the largest user numbers with 76 million members.
Habbo The virtual 'Habbo Hotel' is a place for kids and teens to meet up and chat. It is aimed more at the pre-teen market rather than younger kids, as you have to be 12 and over to join.