Punishments if there caught looking at you again. They have a chance of growing up out of there horneyness having sex at a young age or tempted.
And defiantly talk to them about there puberty. There young it doesn't matter who talks to them. I remember when I used to have boners in the stores, or in public areas often not knowing why it was there & my mom would look at me funny. When she did try to talk to me about it, It wasn't uncomfortable or anything. Now since I'm turning 17 in a few months, It would be a little odd, even though I talk to my friends about it male/female.
EDIT:
I've beat my meat at 12. You know what's happening? You're kids which ever one is having the boners, Is masturbating over you. I'm not even trying to be funny, Seriously. You need to put an end to this or it will effect there mind. You should stop with the kisses on the lips if you are doing that right now. It won't be the same type of kiss you're giving them, that there receiving.
I know a few people who get hard to there mom because of a few things even though they would never marry her they just masturbate to her. I'm not saying that EVERYONE who kisses there mom older age masturbates to them just for people in you're kids case. He purposely watches you & his errection comes..So yeah just to let you know. The same has happen to me & my aunt. I'd always get offers to kiss on the lips I'd turn it down (before puberty) When i got it, I wanted kiss on the lips but I didn't want to ask for it (still young age) I was young & I have no control over my actions now that I've gotten older & see her. I still have thoughts once in a while BUT, I won't go any farther & it's automatic ones from stuff I've done when I was younger, sorta like you're kids case. So yeah not to sound rude or anything..I'm 16 by the way. So i know..
Oh & put something on you're computer that doesn't allow porn. But remember, tell them there gonna get in trouble if there caught looking at porn. Now days EVERYBODY is having sex..I'd know if i was & still am in school.