Generic Chinese bikes tend to be
- Too heavy
- Badly designed in terms of proportions for children's arms, legs and bodies
- Too heavy (how much does it weigh as a percentage of his weight cf yours as a percentage of your weight)
Agree with DABAC: Balance bikes are the way to go. We've been teaching kids to ride via that route since we started our kids club offshoot in June '98 and the total must be in the region of 12-1500. We've taught all sorts from 2yrs 10 months upwards, including a 14yr old severely dyspraxic boy who couldn't even walk alongside his bike without losing his balance/falling over. It took 4 x 2hr sessions but he managed it. Most kids manage it in our normal 2hr session and often before the break at 1 hour.
We have, on occasion,
not used a balance bike or their own with the pedals off, but only when the youngster concerned was absolutely adamant the pedals should stay on (usually older ones). It works.
To get some idea of the right proportions of frame/cranks/brake levers log on to the following.
https://www.islabikes.com/size-guide
https://www.islabikes.com/product/ki...0-large-age-6/
All their bikes' proportions change as the sizes get larger. We've got 22 ranging from CNOC14 model to 26" rigid mtbs and 700c cyclocross bikes and they stand up well to the kinds of punishment our lot dish out, both normal riding and racing. I'm not suggesting you buy one of these - they're pricy, tho' they hold their value remarkably well when it's time to sell on.
I'm not suggesting you buy one - it's not my plastic which'll take the hit
but it will give you some idea of what to look for if you should decide to change his bike. But good luck regardless.