Erm.... Think your all missing a very important point. There is no mention of where the owner or childs parents were during all this.
My parents have a retreiver who wouldnt heart a fly, but doesnt mean I would leave my 3 year old alone with him. Who knows what would happen if she accidently stood on him or pulled his bits (actually he would probably walk of looking sad as only a retreiver can).
All dogs should be treated as dangerous as they all could be, but in the same way that licencing guns doesnt stop people with out licences having them, licencing dogs will have the same effect. All it would do is punish thoes that have done nothing wrong.