Our family will be ending our vacation in Venice (parents and two twenty year old children). We would like fun, memorable, moderately priced restaurants (preferably fish) to end this vacation on a high note. Your favorites and suggestions would be greatly appreciated for two dinners.
Antiche Carampane is very good with an all seafood menu. Because it is near our apartment, it is one of our favorite standbys. Since we've come to know the owner/staff a bit, we've been treated especially well. This is the case with many Venice restaurants. The decor is typical trattoria and a bit cramp. I am not sure your children will find it "fun" and also it is on the expensive side. The antipasti are around 15-18E (can be shared), primi about the same and the secondi are about 20E or a little more.
Trattoria Storica ... A lovely place with great local food and a moderate fixed-price menu (or not). Off the beaten path, but walkable from Rialto/San Marco areas. Very friendly, cordial service with a country-ish feel. Cannaregio, 4858 Ponte dei Gesuiti.
Giorgione ... One of my best seafood meals ever. Closer to pricey than moderate, but worth it. Same area as above.
I don't know what is "fun for twenty year olds” but here are a few good moderately price restaurants that might work. Dining in Venice is mostly seafood and is expensive, therefore, moderately price might be antipasti/primi around 8E, secondi around 18E.
Aciugheta, very close to San Marco, therefore somewhat touristy; large menu of moderately priced food, including pizza, pasta and seafood as well as cicchetti. Cooking may not be top notch, but lively and fun and has something for everyone.
Trattoria alla Rivetta, good seafood near Campo Zaccaria.
Da Alberto, very popular, comfortable and friendly.
Ai Tre Spiedi, good seafood, no reservations
Anice Stellato, fun décor and good selection of seafood and a few meat choices.
Cantinone Storico, near the Accademia with canal tables. Given the location, lots of tourists but the cooking is good and moderately priced.
Antica Besseta, good seafood and vegetables in classic trattoria setting.
Bancogiro, lively bar/simple plates downstair; full service upstair dining room that has a view of the Grand Canal. Menu is mostly seafood but cooking more eclectic than most. This loggia near the Rialto is one of the few areas in Venice that is busy late into the night.
Also search this board, there are many good recommendations for Venice. If you have a specific place, would be happy to help.