Sounds like you just don't like your MIL tbh 🤣 'I know' usually just means I know you're upset because you're a baby... not literally I know what's wrong. But yes... it would probably grate on me too x
Saying "I know, i know" is common but it may be annoying if she doesn't hand baby back if you want her to
The expression is common. But what would grate is not giving baby back. I just go and take the baby from people. They can make it awkward by playing tug of war, but only needed to do it once, now people generally respect that when I say I’ll take the baby, I’m taking the baby.
I think it’s a common thing to say to newborns. I say it to my baby knowing damn well I in fact have no idea. I wouldn’t let it get to you.