The kid needs wedges at the inside to compensate the problem. Basically both feet are are putting more pressure in the external part of the foot. U need to add 1 or 2 wedges to make the internal part of the foot to align with the external one. That's the reason of the nasty pain.

This is what u need... (to start with)

http://www.bikefit.com/docs/WedgeIns...structions.pdf

If you want to test at home just cut cardboard and put it under the insole, just put it around the big toe area. Just a piece of 2mm thick cardboard and not the whole insole, the internal half of it, what u want is to lift just under the big toe. If it works fine great, if you want to go more high tech get the wedges.

Thanks.