Just buy a decent suzuki lt50 or even better a pw50 and training wheels, they've both been going for decades and hold their value well, once your kid out grows it it'll probably get you your money back if kept in decent condition.

 

My son enjoys his electric one over two years now. Powerful motor with 3 speeds settings, battery lasts forever on one charge. FunBikes 800w Black Battery Powered Electric Kids Mini Quad Bike

https://www.instagram.com/p/BDk9v-GhLEv/

They also do 49cc petrol model. FunBikes 49cc Petrol Black Kids Mini Quad Bike

 

A 20 year old lt50 will be better than a new ****** one

Or just get your kid an Oset. I think Im your local dealer as it happens!

 

Depending on age and size, suzuki LT50 or Honda trx90. As good reliable bomb proof quads.
A more race version is the Apache f100s but has to be a standard untouched one.
Chinese 50's are throw away models.

 

I had a Kazuma meerkat, genuine one and it was sound. Reliable, quiet and a 4T

 

Lt50 or Pw50 we have both.