Alright kiddo, so you know how we have a hormone called testosterone that helps our bodies develop into boys or girls? Well, sometimes babies are born with something called complete androgen insensitivity syndrome, which means their bodies can't use testosterone like they're supposed to.
This means that even if the baby has a Y chromosome (which usually means they're going to develop into a boy), their body won't respond to the testosterone and will instead develop as female. So they might have a vagina instead of a penis, and they might develop breasts instead of muscles.
People with complete androgen insensitivity syndrome are genetically male, but their bodies look and function like females. This can cause some challenges for them as they grow up, but with the help of doctors and their families, they can still live happy and healthy lives.