I don't see a moral dilemma here. It is possible that they want to save a child's credit for a child's credit at a later date, isn't it?
There have been recent reports that a credit is a credit, that the CMs help diners figure out how to maximize the plan, etc.
Feel free to share a meal, except at buffets, and pay for children OOP and use their credits later, for either them or for an adult meal. It seems to be standard procedure; the dining plan seems very flexible.