My Son Just Showed Me Red Bumps That He Has

My son just showed me red bumps that he has on his butt, which seemed odd to me. Not just a couple, but multiple, seemed more like a rash but they were pretty distinct bumps. They are only on his butt cheeks and you would not notice it until he took off his underwear. He is 7 years old. He did play baseball tonight but it was not a hot night so he really wasn't even sweaty. I put 1% hydrocortisone on it. Concerns?