If if you don't agree with him mousekilla maybe out of respect to his feelings on the matter you should change the avatar anyway. Personally I don't care but if he feels that strongly about it then changing it would be a mature and considerate thing to do. Of course you don't have to change it to dead rats or whatever it was you were spouting (I hope you were being sarcastic) maybe a pic of the same child holding a herp or something would be better, it doesn't really matter if the pic is offensive or not the fact is someone is bothered by it much the same way you were bothered by body building. Just for curtisy sake a change would be appropiate. Some people feel very strongly about what actions are appropiate for children.
"Only through education do we teach the ignorant that which we love is not evil but wonderous"....