add(child, silent, index) → {DisplayObject}
Adds an existing object as the top child in this group. The child is automatically added to the top of the group, and is displayed above every previous child. Or if the optional index is specified, the child is added at the location specified by the index value,this allows you to control child ordering. If the child was already in this Group, it is simply returned, and nothing else happens to it. If Group.enableBody is set, then a physics body will