Daughters masturbating gone too far ??

i am a older guy
My wife died at a really young age
I have 2 daughters
One is 12 and the other is 14

one year ago I caught them masturbating in the bathroom
i told them it was ok

and that they have the right to do that to them selfs but don't lt other people touch you.

Now just of late i hear all kinds of sounds that have me worried that there doing more the just masturbating.

i don't really want to catch them but it's very wrong if I think there doing very bad things to each other and not stop them.

What should I do????