After Jack was diagnosed, he needed a bone marrowtransplant. They tested Will, who was a perfect match. However, Jack refused consent and said that Will was too young to understand the risks.
The doctors countered that the risks of the procedure to Will were negligible, but Jack held firm. House finally realized that Jack was worn out by trying to raise his two younger siblings, and his illness gave him an "out" to hand them over to foster care without feeling guilty about it.