Tuna Talk..

What is the big deal about telling your 4 year old that his sister's don't have a penis.. that in fact they have something called a vagina? Of course the poor kid can't say such a big word with so many consanents, and is calling it "tuna" (I know.. I know..)
But so what?
I can't remember when I told my older son about our girly bits, but it was right around this age.. And it's not like I sat him down and decided that it was a good day to tell him that boys and girls are different in many ways.. But when he's talking about his sisters penis, and how it looks different than his, then it's time to tell the truth!
My husband thought it was in bad taste to be telling him.. But seriously, like anyone is going to know that when he says his sister has a tuna, that he's really talking about her va-jay-jay, right? Ugh..