My 1st grader was being sexual at school!!

Just got a call from his school, I’m still in shock even typing this out. So the deal is, he was in the boy’s bathroom after lunch. So he was in the bathroom and I guess he got all these other boys to get in one stall. So they all went to pee in one toilet and my son came up with the idea that they kiss each other penises (it was mentioned but didn’t happen) and the fact he was the ringleader of it all makes me furious. I don’t know what to do. My emotions are off the wall, all I want to do is when he gets back is spank him. No lie. He knew what he was doing and I’m just in shock. Please help me be understanding of this because I am mixed feelings right now.