I think kids flying RC airplanes is a touchy subject if the parents are not directly involved.
Its one thing for the kid to operate and fly a relatively safe entry level park flyer and it is something entirely different for him to try to operate say a 20 sized (or larger) glow trainer. The danger level is not comparable between the two. I do think it is great to be willing to help, but this is dangerous and you will be liable if an accident occurs. The best way to help is to teach the mom or dad to fly too and keep them in charge of the childs safety. If the parents are not willing to be involved then I really don't think it is wise to assume the total responsibility for the childs safty and actions.