How to add gun to the model, as when it animate, the gun is dis-positioned.

I've my model fully working along with some 10 animations. but now when I'm adding a gun to the model, i.e. in idle state, it works fine, but when I walk the hands move and the gun it dis-positioned. I've tried making the gun the child of the hands but it is not working. Should I animate the gun according to my other animations ? HELP