Wee-wees and Hoo-hoos

Today when I was picking Isabella up from pre-school, she pointed at one of the dads and this conversation followed -

Isabella: "He's a really big boy. "
Me: "Yes, he is."
Isabella: "He has a really big wee-wee."
Me: "Um... yes... little boys have little wee-wees, big boys have big wee-wees."
Isabella: "I have a hoo-hoo."
Me: "Yes, you do have a hoo-hoo."
Isabella: "You have a hoo-hoo too. I have a little hoo-hoo, and you have a big hoo-hoo."
Me: "Um, yes. Lets get in the car."

I wonder how old she will be when I explain to her that while it's a compliment to tell a man he has a big penis, it's not a compliment to tell a woman she has a big vagina.