Ricky Gervais talked about this in his podcast a while back. That was one of the funniest 5 minutes I've ever heard in my life.
srsly. 5 year olds can barely run straight, much less generate any force with a kick or punch. Watch a 5 yr old soccer game. I think I could take as many as I wanted to until I got tired. The only possible way I could see someone losing would be to quit because of exhaustion and they somehow get you down on the ground and dog pile you and you die of asphyxiation.