Of course there's far more to the story. There always is - not everybody is willing to type out a novel to explain one incident. I'm sure if the grandma was writing this, she would have a very different perspective of it. She would probably highlight that she felt her daughter in law was 'abusive' for encouraging her son and grandson to live a crunchy, holistic, vegan lifestyle and blame her for driving a wedge in the family. Completely ignoring what she'd done, of course.

Everybody has their own perspective. But in the main post, it's not how normal grandmas behave around their family. Normal grandmas who try to 'treat' their grandchildren might sneak them the odd sweet, or even a cookie, or failing all food, might give them a little toy as a gift. They don't a) deliberately give the kid something they know is against the parents' beliefs, b) blame the kid for doing it (wtf, he's four, he'd eat plutonium if you let him) and then c) go on a phone rampage calling the OP abusive and controlling to her son, the dude who married the OP when called out on it. She didn't apologise, didn't say, "I'm sorry, I won't do it again." She tried to turn it around, make it the OP's fault.

The core of this issue is boundaries. The OP and her partner have some and the grandma is refusing to respect them. It's important to enforce those boundaries for the OP's kid because he can't do it on his own. The OP can fully choose to no longer allow their boundaries as a family to be trampled over. Also, please note that it wasn't her who suggested No Contact, it was MIL's SON. When a child wants to no longer contact a parent that's a sign of a more seriously broken relationship beyond what's written in the post. Nobody decides to cut out a parent willynilly.