It may be as simple as letting them know that evenings and bedtimes are good times to masturbate, whereas daytimes are important to develop other interests.
This is a good time to explain further the function of body parts.
If we allow the child's disability to keep us from teaching these concepts, then we will leave him/her vulnerable. It is not enough to just wait and then tell someone "oh, by the way, ask if you have questions." Around this time, young men and women may begin to masturbate.
Just as children learn to eat, drink, sleep, and deal with fear, they can learn to express their sexuality. This activity can be engrossing after bringing oneself to orgasm the first time.
It is the perpetrator who makes the decision to sexual abuse.
Therefore, when teaching people about how to say "No" to unwanted sexual contact, we must be sure to avoid giving the impression that they are responsible if they are abused. In order to teach assertiveness, like saying "No," we have to stop teaching command compliance.
It is important to determine if the person is still enjoying the sensation and not causing harm to him-/herself.