J.J. Williams is a kid whose cancer was discovered after he broke his arm.
J.J. fell while trying to climb the fence with his friend and broke his arm. He was examined in the ER and an x-ray was ordered to confirm. It confirmed the break, but also revealed a mass, which a biopsy showed was osteosarcoma. J.J.'s mother, Michelle, was worried about him dying and J.J. was worried about being bald, but Link reassured them both, saying he had the same kind of cancer when he was a kid and survived and letting J.J. cut his hair.
He has a grandfather who is bald.