Your a dick for letting him take it, so what if you didn't "say" he could, stop him! If it had been my bike he wouldn't have gone more than 5ft from me with it before I stopped the show
If he is a proper Dwarf then i doubt he'll be able to jump. BUT if he is able to then he'll be looking at obstacles on a different scale from yourself so i would imagine he would become very frustrated
not had any weird ones myself but my mate used a piece of brick wedged in his dropout to tension his chain a while back... the brick shattered at the top of a drop gap and he was left in alot of pain on the floor
have you ever tried counter strike on pc? people on that are stupidly good! I can really tell when im playing against someone good on it, they kill me almost the millisecond they see me usually
my only concern would be with the brakes. Especially for someone as young as that, vee's might be difficult to pull with one finger when on back wheel. Get some maggies on that thing and he'll be flying around in circles over your head in a matter of days