Our toddler has discovered the joys of having her hand down the front of her panties. Frequently.
Now, we don't want to tell her that doing so is wrong, but we want to explain to her that there's an appropriate time to be doing such things and an inappropriate time.
How do we best explain to her that she ought not to be doing such things when in public or in company?
All you have to be is honest and straight forward: "If you want to touch yourself, you must do it in private. That is a private time activity. Do you know what private is?"
The question is a good segue that keeps her focused on your real problem, i.e. her timing, and to help you guys from appearing or sounding uncomfortable.
First of all I have a question about the wording of the sentence. The word masturbation seems a bit of an exaggeration. If your son is actually coming to completion then a doctor must be consulted.
If he is just playing with himself, as my three year old is, that is age appropriate. I don't say that to say it is excusable, just nothing to worry about. When we see him playing with himself we simply ask him if he needs to go to the bathroom. He says no and removes his hand. When he is in the bath and touches himself we tell him that a penis is a part of the body, is it private, and should only be touched or played with in private. He is slowly getting the message, although he will tell us it is fun, or it tickles, or it feels good. I understand where he is coming from and I try to simply keep it low key, know he will grow out of it if we keep encouraging him to play only in private.
Oh, I just notices you were talking about your daughter, but I think the same concept applies. Sorry.
