They only abused the child if they made him lie, and to prove he lied (or was given lies to repeat) you have to dig into the family’s finances in detail, which I think will be a losing strategy. It looks mean, and just gives the enemy more fuel to twist things.
Much simpler and direct to point out that what saved his life and the life of his sister was the original unexpanded SCHIP, which Bush did not change. The system worked!