personally, i think it's cases like the OPs is the reason disney made the plan flexible and not separating child/adult credits... think about it... the cost of a kid or two in a child-care center for a few hours (at what, $10/hour/child?) is more than what the parent will consume w/that extra credit...
if you figure an appetizer at $10; entree at $30; dessert at $7 and a cup of coffee for $3... that's $50... how much for two kids at kids' club for 3 hours (minimum, by the time you drop them off, get to the restaurant, wait for your ADR, sit, order, eat, dessert, get back to the kids' club)? $60! disney just made a few bucks on you using your kids' credits for a signature meal... not to mention the likelihood that you'll order a few drinks or a bottle of wine w/that signature meal...
imo, this situation is "no harm/no foul!" (unlike others where you go oop for a $6 kids' meal in order to have a $40 adult meal on a $10 credit)