When I was about 12, I discovered my younger brother had ejaculated.
We weren't so well off growing up so we had to share a room. It was annoying because by then, I was going through puberty and felt very uncomfortable sharing with a boy. He was 10 by that point. I used to noticed that once lights were off, he would play with himself under the covers. We had a great relationship and often came to me when he had questions about school, parents, life, etc. I enjoyed being his big sis.
This one time though, he woke me up at the beginning of the night and seemed really worried. I asked what was wrong and he told me he had done a bad thing.
He proceeded to tell me he had peed the bed. I sprung out of bed so fast! I was surprised, kind of annoyed, and just thought about what mom would say! So i rushed to his bed to check the covers but there was nothing, I inspected every inch of the sheets and comforter but nothing. I told he he must've been dreaming because there was nothing.
He kept saying he did and kept saying he felt wet. I turned the lights on and that's when I saw a tiny stain in his pjs.
I asked him to take off his pjs and he looked at me funny. I told him I needed to inspect them and that's when he pulled them off. His tighty whiteys had an even bigger stain.
I realized he probably had just had his first wet dream. It wasn't much, but enough to leave a mark.
I explained to him that it was nothing and that all boys go through it. That was the beginning of a ton of questions! haha.