L.Z.
My dear friend's son had ITP last year. They noticed that he was suddenly covered in bad bruises, so they took him to the ped. Blood work sent them to the ER immediately.
In his case, they did not treat it. He was checked every week and his platelets slowly climbed on their own, and after several weeks he was considered recovered. He's totally fine now. They suspect that it resulted from a virus that he'd had, and although his mother is now a bit paranoid--naturally--he has not had a resurgence of any symptoms.
It's scary, but most kids do get better on their own. Good luck!