my parents celebrated an anniversary dinner at cinderella royal table restaurant at mk, they have an anniversary package which included a decorated table & champagne glasses*for a fee. the gala dinner at 1900 park fare at the gf is also nice, there is disney characters for the kiddies & you can order specialty desserts like mini cakes or the infamous cinderella slipper for the special occasion. we also enjoyed the salmon for lunch at artist point at wl.
another suggestion would be in room babysitting for your children for a night alone, we have used kids nite out, for a family reunion.
any of the ws restaurants at epcot are great, our personal favorites are le cellier-canada, le origanle alfredos-italy, san angel inn-mexico, les chefs de france. or head over to the boardwalk, we enjoyed dinner at the flying fish & then dancing & karoake at atlantic dance & jellyrolls. or dessert on a fireworks cruise, we did this for a romantic evening through the yacht club.
no matter what you choose hope you have a magical time at wdw! happy anniversary!