how about doing a it based on an already accessable character... like the Tweenies or Bob The Builder - i dunno something the kids can first relate to.
have a few games which do over a few subjects... but structure them in a way that the kids will want to learn.
like say Bob the Builder could be on a building site and have say 3th peice of wood on his right, 5th on his left then he says something like ... "i have 3 and 5 peice of wood, so how many peice of wood do i have?"
then move onto nails... perhaps cutting them in half or into 3.
ya know simple things they can relate to