It's always a difficult question, but the reality is that there is no safety on the internet, and no matter how long someone has been around you can't know for certain who they really are and what they are really like. In the UK recently several celebrities from the 70s have been discovered to have been getting up to all sorts of horrific things, and these were well-loved figures in the public eye - imagine how much easier it is to hide behind an avatar. The only solutions are either to decide not to post pictures of your children, or to post pictures which are not identifiable or in which you have blurred the facial features - there is software to do this, then you can share in relative safety.