i think that you shouldn't teach the kid to play with one finger - because then when you tell them they need to start using other fingers they'll be screwed. Whatever is hardest to do at the begginning is usually for the best in the long run, so i'd get them playing stuff with the proper fingering if i were you; no matter how hard it may seem... the problems with keeping motivation there
I totally agree, the next move is to introduce the ring finger into the mix.
Once he gets a couple more simple riffs (to build his confidence) then the joys of D, E, Am and A will be turning up to challenge him ;)
Unfortunitely due to work pressures I won't be home for 5 weeks (instead of the planned 2) :(
Rob...