One day they were headed out the door and he told his son (probably 6ish at the time), "go empty your bladder so we can leave."

Oldest daughter (8ish): Dad what's a bladder?
Dad: it's a little bag that holds your urine until you can get to the bathroom and let it out.
Daughter: Ohh the hangy down thing (while holding her hand out, palm up and wagging her fingers back and forth)
Dad (laughing): Nope, everybody has a bladder. Not just boys.