L.R.
However you choose to explain it, please don't say that babies reside in mom's "tummy." That's not just wrong, it confuses kids. I know folks who said their children asked things like, "If the baby's in mommy's tummy, how does she have room for food in there?" and "Does the baby eat the food that goes into mommy's tummy when she eats?" etc. Even if you don't get into the sex discussion, at least let them know that there is a special place called the womb where the baby grows and it is not the same as the stomach. I think a seven-year-old definitely can handle that idea.