Your child wants to know how that baby got inside its mom's belly -- and how it's going to get out.
Once you have explained the basics of sex to your child, if his questions lead you to offer more details, don't hesitate. Just say: "During sex, sperm (or seeds) come out of a man's penis and enter a woman's vagina. If a sperm gets together with a woman's egg, a baby starts to grow." Explain that while the baby starts off very small, he'll grow bigger every day inside his mommy's womb. After nine months, the baby will be big and strong enough to survive on his own, so the mommy will push him out through her (very stretchy) vagina or the doctor will take him out through a small cut in the mommy's belly.