The official Dis answer is that YOU are required to keep track yourself and make sure that you use your credits accordingly. There are several places on this site to find spreadsheets and note keeping ideas to ensure that you do not over use the adult credits and if you do it is considered stealing by this community.
The official Disney answer (which is all that is allowed on the Dis?!?!?) is that a child may only eat from a children's menu is one is available. Your KTTW card will indicate the make up of your party (ie 2 adults and 2 children) and that is all that the CM will allow to be used during an individual transaction.
If a child does not eat a particular meal for some reason, then you are expected to use that credit for a child at another time, or lose it. However you are correct, Disney does not track child v adult credits.
There may be other possibilities, but they are not allowed to be discussed here, and many consider them to be stealing.