Everyone in your room must be on the same dining plan.
And Disney would charge your 11 year old as an adult, but you could still order from the kids menu (would be a big waste of money though with the credits).
Options:
1. All of you get the plan and just pick what you want from the menus. If you stick to buffets for your table service meals, the kids can pick what they want from the kids or adults sections. You could also use the adult credits up and share things and then buy an extra kids meal out of pocket. There are also lots of restaurants that have adult meals that are very kid friendly (mac and cheese, spaghetti, pizza, chicken, hamburgers).
2. Don't do the plan at all and just go OOP. If you don't do desserts much or you don't order steaks a lot when you go to restaurants and if you aren't planning on several character meals, then paying out of pocket should be about the same if not less than the cost of the plan.
3. If you are a DVC member (it seems that you are not, but IF YOU ARE), you can go OOP and still get discounts. As long as you have your DVC member card, there are a decent amount of places to eat that give 10 to 20% off. You can get a list of discounts called "Portable perks" at any DVC resort. The list tells you about all of the shopping, dining, and extra discounts.
Most of them are the restaurants at DVC resorts such as Sanaa at Animal Kingdom, Olivia's at OKW, Turf Club at Saratoga Springs. There are several others, i believe Rainforest cafe, fultons crabhouse, and ghirardellis and a few others as well.
Don't feel like you MUST choose a plan if it doesn't work well with your family's eating habits.
