One of my favorite blogs, My Little Mochi, featured this darling typo.
Buddy: Mommy! Come see what I wrote.
["Mommy is a piss"]
Me: Um...Wow... Did you write that all by yourself?
Buddy: Yes. Do you want me to read it to you?
Me: Yes, please.
Buddy: It says, "Mommy is a princess!"
Me: Ohhhh...It does?!
Buddy: Yes, and I didn't have to ask you to help me spell or anything. Now I'm going to write daddy is a knight!
(Technorati link: mochi)