Help!

Hello everybody, I am happily married and have a wonderful family. I don't really have time for sex that much anymore because of my children. My husband starting asking me if we wanted to start getting into it again? The thing I'm worried about is if my children hear us having sex and maybe even walking in when I'm on top of him. Is there any advice so there is less chance of my children hearing us? Also my children are 13 and 15 years old so I'm scared about them seeing me and being scared for life