In theory, at least, the Children’s Online Privacy Protection Act (COPPA) prevents websites from collecting personal information about children who are under the age of 13 without their parents’ permission.
In practice, a simple adjustment of date of birth enables access to numerous social sites. There are, however, a number of social sites available for younger children which might, as a parent, be worth considering. The controls are stricter, giving you a little more peace of mind…5 Fun and Safe Social Networks for Children…