I presume you're talking in the context of anorexia, so if not, ignore the below. You should not be refeeding without specialist input. That doesn't necessarily mean inpatient, it can be done at home, but refeeding after starvation is a delicate process and getting it wrong can be dangerous. Most programmes wouldn't cater to veganism. Vegetarianism, yes, but not veganism. That said, if the child genuinely was vegan, of their own moral decision, before anorexia, then I think it should be accomodated, but that makes it even more imperative that you get specialist input to get the correct nutrients.