Mom forces kids to be vegetarian

Firstly, I have no issue with vegetarian/vegan families. If you believe in not eating meat/animal products and want to do it as a family, that all fine as long as they're properly nourished.
.
That's not the case with this family though. The mom an dad are rampant meat eaters and for some reason refuse to allow their kids to eat meat. If they eat meat, even if away with family, they get spanked with a belt (which I don't agree with in general let alone for something like eating meat). But the parents will gluttonously eat meat and drink milk and have cheese (all things they refuse to let their kids have) but if the kids touch it they get in big trouble.
.
I just don't understand, all I can think of is that it's some big power play over their kids or something. What's your view on the topic?
.
UPDATE:
I don't know what they supplement with. I know they eat a lot of scrambled eggs. That's most of what I know and when they're with their grandma (my husband's great aunt). But I do know that they also don't allow them to eat anything soy because "soy is bad for you" I've actually never met the parents, just the kids because they'd be pawned off on their grandma for weeks at a time, but was told that if the parents found out about meat they'd get the belt. It's to the point the kids at kinda scared when meet is around.
Also the person in first hand knowledge of this (the great aunt) refuses to report and I don't think me reporting would do anything, especially since they live several states away currently (they moved a month ago)