If you are getting 2 rooms in one reservation, others have said no you cant do that. All rooms on the same reservation 'have' to be on the same plan. I was thinking about you could do one room in your name and one in the other adult's name but that wouldnt get you dining for both adults. The plan can 'ONLY' be used by those listed for that room. Each reservation 'MUST' have an adult. So you couldnt book a second reservation for the kids unless one was 18. I put the words in quotes because these are rules I have seen/heard here etc but have not officialy read in disney literature.
If it helps any, I was told two different things by the CM's I asked if two of the kids could share one plate (ts or cs, obviously not at a buffet or otherwise all you can eat) and then share one again later. CS really shouldnt be able to be a problem as far as I can tell. Since they are picky and eat little at a time. One said everyone on the plan must have their own plate. The other however said just tell them when you are being seated that you are paying separately for the other one, or both kids. Buy them a drink, or whatever. but save their ts for later. Since you basically get 2 meals a day this give you a third for the kids in my case a good thing since they eat so little. I am wondering if I can take out with these left over ts's for the kids to eat while we continue to go around the park. They also told me that the meals arent regulated as to who they are used for,as long as it is someone in the same party. So When discussing this with the CM (we have 2adults &2kids) she suggested something like this-Eat at la'cellier (?) where they have a $5 kid meal,pay for this separately, let the kids split it. If you do this at two restraunts, you can all go to one of the dinner shows another night. This does cost an extra $10 + tax & tip. But If you want that it may be in the end a cost effective way to utilize the dining plan. I havent made ps's this way but I have been planning on going through menu's etc and thinking it out.