My favorite that my then 3-5 year old said was "willn't" instead of "won't". It was so cute and made perfect sense, so I hated to correct him! I kinda miss it now . . . .

My mom says that, when I was little, I used to say "what-ya-do-me?" instead of "what are you doing?" My mom still pulls this one out for use every once in a while!

She thought she could, so she did.