Wonder if this kid has the wrong brakeset in there, long vs short brakes.

Second detail. the wheels you are putting in there are like 120 mm wide vs 130 or 127 of that frame??? the rear end in the yellow bike looks really bad and pretty much is bent in. You can do +- 2 mm but if you are putting a 120 mm wheel in that bike then clearly you will have problems. So far i can see you have the wrong hub spacing in that bike.

Whats the spacing in the frame versus the spacing in the hub?

Good luck with this one, IMO you have the wrong wheels in that frame to start with, thats the root of your problem. (Whats the spacing in the frame versus the spacing in the hub?)