After living with my SO and SD9 for a few years, I've realized just how much I despise baby talk. It makes me want to rip out my ear drums!
I know the baby talk has been a learned way of communication to get attention...but GEESH! She is almost 10 and still intentionally mispronounces words or speaks in a baby higher pitched voice around SO. When he's not around, she speaks clearly and in a regular voice.
My 9 year old step-daughter is super annoying. I don't remember my son being like this when he was this age. I even asked my mom if I was annoying at the age of 9 and she said no, not even close to how obnoxious my SD9 is.