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.
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However, I just like to give everyone the benefit of the doubt, and felt your original post felt accusatory to people you had no negative knowledge of. I'm not a big fan of letting one apple spoil the bunch as it were. Besides, what's the worst that's going to happen? Someone is going to see your child, and then what? Can't they be seen at gym, school, public, etc? Everyone has a different comfort level on this sort of thing, and I understand and respect that. I hate fear, and have tried very hard with my children to see that they don't fall victim to it. A good head on their shoulders, some common sense (not so common anymore), and an open mind is how I try and have them face people and the world. Having said that, I understand and respect your decision, but hope you will still join. As Mama Duck has said, there is no requirement or mandate to post anything here. Read, ask, learn. 
