The numbers I posted are real numbers, from 2005. Do you have any basis for your $4 figure for kids CS meals ? The snack is valued at around $2 and the child meal plan costs $11. Assume Disney allows $4 for a child CS meal. That leaves $5 for a child's TS meal.Doesn't sound right to me. Character child meals cost around $15 with tax and tip.
Using the same ratio that's used for adult meals I'd expect something like $2.25-$2.50 for CS meals and $6-$7 for TS meals. Back out the $2 snack and the cost difference betwen a child meal plan and adult is almost exactly 4 to 1.
It really doesn't matter, Disney doesn't let you upgrade/downgrade credits from child to adult or from CS to TS. Given the problems in just separating credits I wouldn't expect to see these kind of refinements any time soon.
Your question is valid, should Disney offer a way to upgrade child CS credits for adult. The ratio would probably be 4 to 1 and I suspect guests would, wrongly, think Disney is cheating them.