Platetlet question

A 13 month old was rushed to the hospital last week, due to bruises appearing in various parts of his body when he awoke from his nap. He had blood vessels bursting in his body. After some test at the hospital the dr's found his blood platelet had fallen to 2. He was given medication where the platelet went up to 5 and then given steroid where it went up to 8. He is being tested for leukemia, lupus, etc.

Just curious to see if anyone has any clues about what could cause the platelets to drop that low. I've been trying to figure it out but not sure.