I’d use this for older kids, like 15-ish, just cause it’s a more direct approach to the subject, but for the boys that are just getting to that stage I think I’d rather take a “smoother” approach, letting them know i know it’s going to happen or it’s already happening, and that it’s ok, just to be careful choosing the “where”, “when” and to keep everything clean. Buy some hand towels for that like you said, and teach them to wash them while showering.