Moos cannot even protect their own famblee...

when their own famblee is dangerous and destructive...
Moo complaining that MIL called CPS without any rational justification. (Let's assume that she is correct: the complaint was that the child appeared under-nourished. Said child is correct weight for height.)
Moo was told to eliminate contact with said MIL because she has gone over the line, change phone #, etc. Moo fights suggestiong because 'it is fambleee' and duh is a wimp. 'don't be mad mummy...'.

Stupid moos.

They even interfere with each other. Do they have no boundaries? Worry about your own damn shit. I'd move away.

If someone tried to pull that li'l number on a childed version of me, that would be the last time they saw the kid. Never have a pissing contest with a skunk. Toxic: avoid.

That is also why not to marry mamas boys. It may give you (temporarily) a feeling of superiority and give you a stage for your drama queen acts but when MIL is destructive, you lose all. Mostly the child.
When hubby cannot stand up to his own moo, and MIL makes a false charge stick, you will go to prison watching hubby with his moo (holding the baby) and hubby will be saying 'don't be mad mommy'.

If moomie was innocent, then what grandmoo did was unforgivable and I would move as far away from her as I could, with or without her candy assed son. These types of power plays will not stop, but will only intensify in frequency and severity. I would have asked her what she had hoped to accomplish by this and did she realize that the grandpup could have gone to strangers in a foster care system? A lot of famblees who call CPS out of revenge, including some of the brats themselves, never think through what it is they are doing. If CPS didn't act on this particular report, then you can bet that these people are "red flagged" and any little thing could cause CPS to descend upon them in the future and whether it's warranted will be of no consequence. If it's not feasible for her to move, then she at least needs to keep that kyd as far away from grandmoo as possible and always be present when grandmoo and grandbrat have contact. There wouldn't be any sleep overs at granny's house, that's for sure.