In Canada, PSL Karting offered a CRG/PSL RS5 28mm frame that was purpose-built for the LO206, and run to Canadian specs (50″ max width, 6.0 rear tires). I’m not sure where you’ll find them in the USA.
If you’re set on CRG and LO206, that would be a very good option, as the cost of the chassis was much lower than a typical “TAG” chassis, by using 40mm rear end, 17mm front end, older brake system, only 2 rear axle bearings / carriers, etc.
The downside to that setup is that it isn’t suitable for moving up to other classes with more horsepower.
The CRG KT-1 is a 30mm 2-cycle chassis that can be setup to take a LO206, and should work just fine for a bigger guy, or run at 55″, 7.1 rears, etc – and can still take a more powerful engine package if you want.
For the step-son, a cadet kart would probably be the way to go.