If you’re just going to assign an arbitrary token amount to charge for the food then how will that teach the kids the value of money? And since the kids themselves wouldn’t be the ones actually paying for the meal it’s still a disconnected symbolic gesture unlikely to impart any lifelong lessons. You’re going to be spending more effort and potentially money in tracking and enforcing payments for the meals than what you’re going to recoup by (under)charging for them. How about, since everyone is already paying taxes toward education, we just allocate some of those funds to providing food for every student/child if they are actually intended to be the future productive members and leaders of society?

I would think a better method to teach the value of money is to explain the economies of scale and couple that with showing how much planning and work goes into providing and preparing the “free” meals so they aren’t taken for granted as just being manna from heaven.