Your body can produce carbs from the food you eat.
You have a choice, you can either eat a lot of carbs, or you can eat a lot of fat. You cannot eat both, and that’s what gets people into trouble.
So yes, a plant-based diet that is low-fat can be healthy, provided you make sure you get the essential amino acids.
Uhhhhhhh... not so much.
Getting "the essential amino acids" sounds good on paper, but no. Especially with kids.
They also deprive themselves of the crucial fatty acids and trace minerals.