Explaining birth to children

Mandi 😈💀 • Expecting #2 August '15!
I work at a school and am currently listening to preschoolers talk about how they were in their moms tummy and then they came out. I started wondering how I was going to explain this to my own kids when they get older, and wondering to myself if I would use technical terms like vagina or just say "nicer" words like birth canal or something. I won't personally just use "cutesy" explanations like babies come out of mommies belly button, but I was wondering what you were going to do when your kids get older, or what you've told your older children about their siblings and themselves.