Sex File: I'm scared to wake the children, so sex is off the menu

"Researchers found that when they exposed babies to white noise, the likelihood of them falling asleep increased more than threefold, from 25 to 80%."

Noise machines obviously block out sudden background noises such as an ambulance siren or a door slamming - and they block out the sound of adults having sex in the room next door. 

My husband and I have young children (two and four) and although I expected neither of us to want much sex at this stage, we do.

The problem is that we have a small home, and I'm so anxious about waking the kids up it kills my mood before we begin. How can I break the cycle?