I agree, if you want to eat at LT, then book the lunch. The lunch is menu selection, so you child can possibly order from the menu. If you go to any buffets, your 11 year old WILL be charged as an adult.
For example: 2 years ago the age for buffet was 11 and under as a child. We booked the Cape May with our grandson 10 years old. We made the ADR in May, but then Disney announced that starting July 1 the age would drop to 9. We didn't know what was going to happen, especially since he was legite when we made the ADR. We went to Cape May and explained the situation and the manager said, their policy is that we would he would NOW be paying adult price. We left and ate elsewhere and did complained to the front desk. We knew the rules had changed, but everytime we asked dining if the current ADRs would be grandfathered in, they would tell us that we would be paying kids prices. Back then he would've only eaten pizza and chix strips. He's a bigger eater now, so paying adult is OK with us. So if you take your 11 year old to any of the Disney buffets, it will cost the price of an adult meal. We skipped buffets with the grandson for 2 years until his appetite changed. However, at many TS restraurants you can order a child's meal in adult serving size for an additional amount. We did this often.