My Family Problem

I am a newly single mother of 2, a boy 12 and a girl 9..my problem is that my son is I quess what you would call a exhibitionist, he likes to sit around and rub himself while watching TV and he likes to do it infront of me and my daughter. it is like he wants for us to see his dick. He normally wears just shorts around the house with no underwear.and will just play with it anytime he wants too..I do have to admit that it turns me on sometimes with him playing with his erection in front of my daughter and also when my niece is over it doesn't stop..she is 8 and he will do it with her watching as well..I sometimes can't take my eyes away from it..He is not very big in that department but noticeable..