A suggestion if you plan on leaving toys in the TH all winter and not moving them would be to lay a piece of 3/4" plywood under the wheels that are on top of a area of floor, not near a floor joist or cross member.
This would help spread the load to the cross member and possibly not bow the floor material(osb/pressboard-thin plywood)as much or at all. Make sure the extra plywood spans from joist/cross member to the next cross member.
Plywood in winter-moist areas will sag from weight over a extended period of time, leaving you with those small dips in the floor.