When my kids were in public school there was a kid like this. Little boy whose parents forced him to be a vegan. He was Significantly smaller than the other kids. It also effected his mental capabilities.
Big surprise. /sarc
IMO parents who do this should be charged with child abuse.
They were the weediest, sickliest, pasty-skinned little kids you ever saw. I don't remember their intellectual capabilities -- but they caught every bug going around the school, never played on the playground, pretty pathetic.
The dad of one of the other kids in carpool was a pediatrician and a close friend of my parents, and I remember them discussing in my hearing what they could do about it, but not whether they were going to try what's now called an "intervention" or report the parents to somebody. Never heard what came of it, all of that was way above my pay grade.
But the pediatrician said that vitamin supplements and stuff like that wouldn't do the trick, that there were nutrients that growing kids needed that you could only get from milk, meat, fish and eggs. He said once you were finished growing, you could abuse your body a whole lot more and get away with it.
My Dad’s sister had a grandchild that was being fed vegan and was skinny and always hungry. My aunt kept feeding him real food when the parents were gone. He survived the ordeal and the parents gave up vegan a number of years ago.