What is it with kids and bathrooms?

Seriously. What is it with kids and bathrooms? I can't get my kids to voluntarily walk into the bathroom. They make up every excuse in the book as to why they don't have to pee or why they don't need to brush their teeth. Yet, if I walk into the bathroom, it's like Mommy just entered a toy store and didn't invite them.

"Can I pleeeaaaseee come in?"
"Mommy! What are you doing in there?"
"Mooooommmmyyyyy??? Where aaaarrreee yoooouuu?"