He's 13. Any 13 year-old is going to be masturbating, and probably to porn. What did you expect? Firstly, congratulate him on his first steps into adulthood, and that adulthood comes with a few extra responsibilities. Tell him that you found his porn and tell him to try not to be embarrassed. Tell him that masturbation is a perfectly normal part of adulthood and that what he's doing is perfectly fine and is actually very healthy and good for him, but that he needs to follow some simple rules so that it remains appropriate. Tell him you're sorry for not explaining the rules to him sooner. Tell him to find a more secret place to hide his porn (preferably high up in a closet so his sister cannot reach it). Tell him to make sure his internet porn is always kept off the screen when he's done with it and that any downloads are kept in a secret folder in a private file. Tell him that if porn magazines are under his bed in a place where you can find it, his sister may accidentally find it and she's not ready for that level of sexual awareness. Tell him to stash them more carefully until his sister is at an age when you're ready to explain such things to her. As for your daughter walking in on him masturbating, that is always a possibility (though unlikely). So what? It's not going to scar her unless you treat it as if it's some kind of sexual abuse. Masturbation is perfectly normal. You need to treat it as any other normal part of growing up and teach your kids that it's no big deal. Look, masturbation is just like going to the toilet. It's something most adults are going to be doing. Teens are going to do it at least once every day, usually much more. So treat it just like going to the toilet - explain to him that it's a private thing, to close the door while he's doing it. Explain to your daughter that her brother is becoming an adult and that he needs private time for sexual development. Teach her to respect closed doors, and explain that if she accidentally walks in on him playing with his penis or looking at pictures of naked people, just say 'Oops, sorry', then close the door and leave the room. It's not a big deal. You really should have brought these things up BEFORE he started masturbating, so that it never became a source of embarrassment. And your daughter can handle enough knowledge to deal with any issues. Kids aren't delicate flowers - they can understand concepts like these - it's really not that difficult unless the parents make it so.