...to not want MIL to refer to my son as her baby?

[jumblequeen]

I should say from the off that I have a very good relationship with my MIL. Apart from this one issue, I think she's absolutely wonderful but that almost makes it harder to broach the subject. She keeps on saying "my baby" when referring to my son and it's really getting on my nerves. He's not hers, he's mine! I may have a touch of precious-first-born syndrome here but still... AIBU or should I say something? If so, how?!

next time she says "where's my baby?" tell her he's at work but should be back by dinner time .

"But now it seems you are saying that she deliberately calls herself 'mummy"

We don't know OP didn't have a slip of the tongue and didn't notice.
The OP seems rather childishly determined to take offence, so it could easily have been a slip of the tongue the op misinterpreted.
When you have spent 10, 20 or 30 years calling yourself mum, mummy then it slips out very easily

Also-people can only get away with silly behaviour while the DC is a baby. They will then be quite clear in 'I am a big boy and not a baby' and they will know perfectly well who is mummy and who is grandma. It isn't worth fussing about.

My mum sees DS she says "hows my little Sammy" He is 15, 5'11 and size 11 shoes. He just gives her a big grin and a bear hug