Go with a Honda XR-50. Easy and reliable. He will want to ride forever.

I would buy a XR 50. My son is 4.5 and has a pw 50. He is big for his age at 50lbs but last time we were riding he swapped bikes with another kid on an xr 50 and he did great with the bike just left in second gear. He was a little tippy toe but since he has been riding over 1 year he did just fine. The other kid was almost 8 and he still fit on the XR 50.

My son also liked the foot brake on the xr50, he had no trouble working it. His pw 50 has 2 hand brakes and that was what held him back when he first started riding at 3, he could not properly apply the brakes so I had to keep him in a field and watch him close. he could ride, control throttle and balance excellent but just could not squeeze the brakes enough to stop on a big downhill.

I would also consider a PW 80, 3 speed auto and if he can touch/ pick it up much more bike to grow into. I have a pw 80 ready and waiting, my son just needs a few more inches. He will be on it in the next few months as it is not much bigger than an xr 50.

I would not consider any of the race bikes, polini, LEM, KTM, unless he already really knows what he is doing, and wants to get into racing.

hey i have a 2005 ttr 50 e start. ridden by a 6 year old girl. asking 1000 obo. located in lubbock texas phone 806 747 6318 or scottyford_2@yahoo.com

Started my 7 year old girl (she is small for her age, only 40lbs) on a tiny chinese 4 wheeler cause she was not too good on 2 wheeler yet, within 2 months she was on a PW50, good size and easy to ride, but dad had to start it all the time for her. We soon got a TTR50 electric start. Now wer'e talking! Perfect!
If choosing from the 2 you list, I'd get the honda 50 over the PW. Its auto clutch and has the brakes in the right places! PW is hand brake only.

I would get either a china clone or a crf50. Training wheels can be bought pretty easily. Wheels for Tots or something like that offer some but they are pretty expensive. If its her first bike... you may want to get her local lessons. Motocross University in Arlington teaches out at village creek mx park weekly. Their site is www.motocrossuniversity.com Hope that helps