It would be better if semen did not stain as it does. When I was 12 and began to have "wet dreams" and then later started to masturbate, my mom (it is just us two) knew it. We talked about it — my mom is cool. She said that when I masturbate it would be better if I ejaculated onto a paper towel or napkin so I could throw it away. I had been using my socks, T-shirts, and undershorts. She understood that "wet dreams" were different, and I explained that sometimes when I masturbate it is not planned, so I use whatever is there. She also understood that, but now I keep a roll of paper towels near my bed. 
- age 13, Florida