God's grace distribution was explained in Chapter 4.
Basically, blue-robed temple members have their own attendants and cooks. They eat first, then their attendants get the leftovers, then adult gray-robed members get to eat, then the baptized children, then the pre-baptized ones. Basically, the pre-baptized ones are the ones who are most likely to starve because there is not much left. God's grace food is distributed equally. Pre-baptized children aren't even regarded as human, that's the harsh reality of the temple.
Myne could use her own earned money to just distribute more food, but all of this has already been discussed in Chapter 8 and 9. She doesn't have unlimited funds, and she has her own plans to make books, so she can't just use all her money to feed them. This is why Lutz in Chapter 9 suggests alternatives to make them become less dependent on the food trickle system of the temple, like setting up a workshop to earn money, letting them forage in the forest and teaching them how to make their own soup. If the orphans can feed themselves, the God's grace can be distributed to the pre-baptized children, so they won't starve. The kid complaining wouldn't have starved, as he would have gotten the rest of the food that pre-baptized children couldn't get. Baptized children usually get work as apprentices in this world. In the temple, unless they are working as an attendant for a blue-robed member, they do nothing otherwise. So Myne is trying to make them work and rewards them for this. It's not part of the God's grace. Child labor isn't not only not frowned upon, it's necessary to survive.