a mate of mine went the european alternative for his boy, he just turned 6 and they stuck him on a KTM 50, ok double the coin than what a china alternative is worth, but my GOD, what an awesome machine! No gears to worry about, the build is FANTASTIC, both front and back brakes are on the handle bars, front end is a genuine marz. unit, starts first kick every time, and still has enough power to pull an adult(80+) kg upto 65kph +.
FREAKING AWESOME.
but as for a china bike alternative, id be looking at the crf replicas, like the atomik 70cc, pitpro 110cc, something with a small wheen size(10 inch) will keep the seat height relatively low for the little fella, yet will still have enough height for you to have a 'test ride' every now and then!
alternatively have a look into the electric bikes available, or around the same price as the KTM, Oset have some GREAT bikes designed for kids under 10years that are electric powered but still capable of providing ALOT mroe fun than their petrol counterparts, just think, being able to run it down the local park legally, or around the back yard with NO NOISE!
OSET Mini Electric Kids Bikes - Store
Keep us informed of what you do end up with deciding to go for, and update us on how the little tacker goes!
regards
Sp33d.