The floor is a nice place to be when you're trying to be quiet and have intimacy. You can't hit your head on anything, and you have more space to spread out.
The more physical control you both have, the less likely you are to moan and groan.
If kids don't see any action, they become disinterested. If you get all hysterical, they won't leave.
A kitchen table makes an ideal location because she's sitting on a high surface and you can enter her readily.