We are trying not to be obnoxious with our use of UK terms when it comes to the baby. Some things just roll off the tongue more easily. Also, we've been way isolated since moving back to the States, so we haven't exactly heard people use the American terms.
Here are some baby-related British words we've adopted. We probably sound like jerks when you hear us in public, but we aren't really in public very often ... so I guess it's cool:
Pram. It's just so Mary Poppins! I love taking the wee boy off for a walk in the pram.
Nappy. Diaper sounds medical and weird to me. It's much more cute to change a nappy.
Poppers. As in, I prefer the nappies that have velcro, as opposed to the poppers. Or, "This outfit has too many poppers for my arthritic hands!" Poppers are snaps, if you don't get it by now. How cute is that??
Lie-in. This is the equivalent to sleeping in, except you "have a lie-in." We don't actually use this one anymore, though, because who ever has a lie-in when you have a baby?