This is some next-level messed up reasoning. They then went on to haughtily explain how they're not taking him anywhere until he is. No trips, no aquarium, nothing (all because the kid's dad's family are "crazy anti-vaxxers").
How entangled and selfish does one have to be in their own cognitive dissonance to hold political beliefs over their grandchild's head? Poor kid... Grandma is lib AF! I had to walk away mid-conversation because I didn't want to cause a scene. It was my first encounter with someone that hardcore and I didn't know how to handle it without wanting to say very mean things. Sad, sad, sad!
Sad but the child is better off not having contact with said relative. It's so sad but honestly life is better without control freaks and narcissists.