I would say unless they get really excited about the characters, there is not a must do- unless you are doing a dining reservation to get into a reserved section for evening entertainment. For us (DD is 12), Minnie's Breakfast at the Plaza Inn is still a must do because there is a good variety of Characters there (They vary, but we almost always see Minnie, Pooh, Tigger, Fairy Godmother, Hook, Max and at least a couple of others). We love Café Orleans, and for us it is a must do for the food-- but I would not call it a must do restaurant for everyone. Blue Bayou the atmosphere is great, but we don't find the food worth the price. We have been there a couple of times and then we dropped it off our list- we are satisfied with just riding POTC through the restaurant. DLR has such good counter service options, that we don't really find the need to do a lot of dining reservations. If you want to look at all the menus for the restaurants, you can find them at the allears website.
If Fantasmic or World of Color are playing during your trip and they are important to see, then a dining package would be considered a must do for us. It makes it so much easier. Really, if you decide to splurge on something and World of Color is back and has a dessert package- that one would probably seem like something special to 16 year old girls. You actually get to watch the show from a table and chairs- and you are served desserts and drinks (non alcoholic for minors). You might not want to spend that much though when it is not even a full meal.