Do you think that I am out of line to tell him to talk to her and tell her to treat him like an adult?
In my opinion, I do think you would be out of line with a comment like this. It's proven throughout history that the child and the parent of the opposite sex are closer in the parent/child relationship. Just think of the terms "Daddy's little girl" or being a "Momma's boy". Also, it plays very strongly into the Oedipus complex (where subconsciously a child will end up looking for a partner with similar traits as the parent of the opposite sex. Wierd, yet often true).
THAT is the reason that she uses pet names with him and not with her two daughters. They are subconsciously closer than the mother with the daughters. I see it in my family, and in every other family with kids of opposite sexes that I can think about. Think about yourself or your other friends.
Also, just the fact that they are parent/child should be enough to allow such stuff as pet names. I know I'd be freaked out if my mom started calling me by my full name every time she was talking to me. It's not normal. It's too impersonal of a name for someone like a parent to use. What do YOU call him? Do you use pet names for each other? If so, wouldn't it be wierd for you to call him by his full name anytime you needed to talk to him, "Charles, what do you want for dinner? Charles, the bath is getting cold. Charles, how about going away for the weekend?"
She may be talking to him like he's 15, but you have to realize that in HER eyes, he'll ALWAYS be her little boy. Whether he's 15, or 50. You'll understand better when (if) you decide to have a family of your own.
Alexi