what size of binding do i need for a kids...
what size of binding do i need for a kids 7.0 snowboard boot will a small work?
Custom Smalls fit 4K - 7K (kids sizing)
Burton men's Small bindings fit Size 6 - 8 (men's sizing)
So, I guess the question is whether he's in a kids boot or a men's boot. Hopefully this helps!