What is it with 2 year olds?

I know it's been a while but life gets so busy. My daughter is 5 now, and I have a 2 year old son. The 2's are so much fun! My little boy is just as silly as my daughter. What is it with 2 year olds and butts? Every time my son see's a naked butt he's got to stick his hand in it. You gotta watch your butt when Emory is around. :)