My Man and I have three kids, I'm not going to say that they make it "difficult" nor am I going to say they don't effect our sex life.
When you decide to have children (and it's a big decision) your entire life changes. The way you eat, the way you sleep, whether you work or where and how you work, where you live and of course your sex life changes.
Our babies shared our bed, but we would gently put them in the cradle or crib, after they were sound asleep when we wanted to have sex. We taught our children very young (as soon as they could walk) that you knock when coming up to a closed door (we never lock doors in our house) Our children always (usually) knocked before coming into our room. We also, once they were old enough, once they understood, would let them know when we didn't want to be disturbed "unless there is blood or fire" at certain times. Yes, kids know their parents have sex. They don't need the details, but they do need to be respectful of "Mama and Papa Time."
Our youngest is 13, and our middle child is in Grad School and still lives with us (the oldest one is moved out) and sometimes we still have to quiet down, when the kids stay up later than we do. We also have a new rule that they are not to use the spare bedroom (used to be our nursery and is right across the hall from our room) after Mama and Papa go to bed. (It makes me nervous, as the room is so close to ours, I don't want them hearing, and I can't relax when they are in there. They are 8 other rooms to hang out in.)
Like with everything else, you adapt.