Stay Smart Online
If someone your child doesn't know sends your them a friend request on Facebook or Twitter tell them they should not accept it. You don't know who they are or what they could do. Make sure they change their password and watch what links they are going on. Some of those links they might clink on collect their information and they now have their information and can do what they want with it.
Make sure your children are reliable on what they post and do online? You should be able to rely on your kids. If you can not rely on them what you can do is put a password on your computer so that they can only go on it if you allow them to. You can give them like 20 minutes on it. While they are playing you could watch them or stay close while they are playing.