Well is this normal and how can I stop it from happening so often!!?

My Penis gets erect very very easy!! with any 1 or anything sitting in my lap or brush's against me i get hard, no matter who or what it is!! does any 1 else know any 1 this happens to!! its kinda embarrassing and gets in the way when your son or daughter ask to sit in your lap and you have to tell them no!!! and if your out in public just shopping or going for a walk than u have a buldge going on its just weird!! how do i stop this??