Where's her penis?

I know, I laughed too when I first heard Boy #2 say that. Actually he demanded to know as he peered over my friends shoulder. She was changing her daughters diaper and Boy #2 was there to, I don't know, offer assistance, he being just out of diapers himself and a little brother still in them I guess he thought my friend, a new mom, could use some help from an all knowing three year old. But when he leaned in for a look see, his jaw dropped to the ground. His eyes grew wide and darted around the immediate area, frantically searching, "Where's her penis?" My friend gave me a helpless look.
Honestly, I was surprised Boy #2 was just finding this out, I thought his older brother would have told him by now. The kid knew more about the birds and the bees by the time he was ten than I did. An older brother with neighborhood friends brings information much sooner than necessary.
I hesitated when the question was asked and my friend, a pro-active, take charge kind of person, explained the difference between boys and girls to my son. She never let's me forget this.
The next day I decided I needed to be more responsive for my boys inquisitive little minds, so I sat them down and said, "All penis questions go to dad, he has one, I don't. If it's an emergency, I'll try to answer to the best of my ability, but the questions will be run by dad at a later time and date."