So I'm a first time mom, but my siblings are all much younger then me. The other day my little brother (6) asked me where my baby was, so I just said in my belly.

"Kiki(me) where's your baby?"

"It's in my belly right here"*points at belly*

"Do you know where babys come from Kiki"

"Haha, yeah, I'd hope so"

"A mommy and a daddy want a baby, so god puts a balloon in the mommy's belly, then it gets bigger until it pops. Then when the balloon pops a bird brings the mommy and daddy a baby"

Then my little sister(4) joins in.

"No! It goes, a mommy and daddy kiss, then when they kiss it makes a baby in the mommy, and when the baby is bigger the mommy poops it out."

I tried to vaguely explain how it really works to them, but I don't know how my parents want to handle it, so I didn't go into detail haha