My 12 year old who is about 5' rides a ttr125l. It is great for trails. He tried a KX 100, but it scared him on the trail. He hasn't been riding as long as your kid but he is not to bad.
I have to vote for a ttr125L, KLX125L or a DRZ125L and than do all the mods over time. Makes for a great trail bike. Remember it's not the bike it's the rider. I let my friend ride my son's bike once in a while and I have a hard time keeping up on trails with my KDX 200. He is a better rider than I.
Besides, you might enjoy ripping around on that bike too.
I have to vote for a ttr125L, KLX125L or a DRZ125L and than do all the mods over time. Makes for a great trail bike. Remember it's not the bike it's the rider. I let my friend ride my son's bike once in a while and I have a hard time keeping up on trails with my KDX 200. He is a better rider than I.
Besides, you might enjoy ripping around on that bike too.