If you are looking for CS...
Sunshine Seasons has vegetarian chinese, salads with no red meat (seared tuna in one, beets and cheese in another), or a grilled salmon dinner for adults; kids can choose mac and cheese or pb&j as their entree to avoid meat.
Of course, Yorkshire Fish Shop sells fish and chips. Kids eat the same thing as adults here, since it's all that is on the menu.
If you decide on DHS, Pizza Planet can supply you with cheese or veggie pizzas.
If you are seeking TS...
We once did Garden Grill with a pescevegetarian (doesn't eat meat but will eat fish) and they brought him platters of the catfish from their dinner since he wouldn't be eating steak or turkey with us - if you spoke to the server, I see no reason why they would not be willing to do a similar thing and bring your family just fish. It may be a little pricey for you for a catfish all-you-can-eat, but they do have characters for dinner?
Rose and Crown has fish and chips and a yummy vegetarian curry; kids can pick mac and cheese or cheese pizza.
Nine Dragons has a couple of fish/vegetable offerings for adults, but for kids there are only a couple of choices and if I remember correctly they are chicken and meatballs.
Chefs de France has some lovely seafood and vegetarian entrees (and that grown-up mac and cheese is good), and they have a fish entree for kids, but their pricing is not exactly 'inexpensive.'
At DHS, 50s PTC has tuna casserole (a lenten memory for many members of our family

) for adults and fish for kids.
Also at DHS, the Sci-Fi Drive-in has shrimp pasta and a seared tofu dish that I enjoy more than the burger I once had there; kids can pick cheese pizza or mac and cheese.
Mama Melrose, as you already mentioned, is an option too - and can be booked with the Fantasmic package if that interests you, and if they are offeing it for that night.
HTH!
