[wdfifteen]

The angled wheel mount is responsible for the caster angle, which helps the steering auto-center. Turning the wheels does lift the chassis up, and letting go of the steering wheel should allow gravity to lower the chassis and let the wheels return to center. I don't know why this effect isn't symmetrical on your cart, but that may be the problem. Caster does slow a car down, but it helps steering stability, which is probably a good thing on a kid's cart.
From the photo it looks like there is considerable toe-out of the front wheels, but that could just be the camera. I would check the tow and check the caster.