A baby's digestive system starts to develop before you might even know you're pregnant. While their first bowel movement isn't until after they're born, babies do pee in the womb and build up waste ...

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to CuriousKidsUS@theconversation.com. Much of the food you eat is absorbed by your ...