There are some really good breakfast/brunch/lunch/cake places in St Helier that you all might like - check out The Yard at Jersey Museum, La Bouche in the covered market, Cargo or Locke’s. Upstairs at Anley Street does great sharing pies for big appetites, and other very good food. The Square is good for steaks and seafood. JB’s does craft beer and barbecue and also hires out ping pong tables. Seafood is great in general in Jersey, and Portuguese food is definitely a good shout, as is Thai.
Don’t however be tempted by the Thai food at the zoo, although the rest of the menu, including the pizzas, is decent. If you’re at the War Tunnels, head to St Ouen’s Bay and eat at El Tico, La Braye or Sands, all have good burgers/seafood/pasta options and great views. If your teens would be up for it, they can take surfing lessons in the bay too, or swim anywhere around the island. You can also do coasteering (again, book ahead),
paddle boarding, or foraging - check out Kaz, who is brilliant. https://wildadventuresjersey.com/ Head up to L’Etacq in the north west for fabulous volcanic views at low tide, or Green Island in the south east.
Book your boat trip well in advance and I’d recommend Jersey Seafaris - the Minquiers or L’Ecrehous are fun. Have a plan B in case the weather scuppers that. Elizabeth Castle ie fun with the duck boat but I find Mont Orgueil the more interesting castle, with art installations that keep interest up (make sure you find the Wheel of Urine). Jersey Museum is a good wet weather option, as is the Maritime Museum.
A lot of the pubs in Jersey will do a standard pub meal but none are that interesting - you probably wouldn’t go wrong if you wanted something with chips though, and the buildings can be lovely to sit in. The beach cafes will do you a great crab sandwich or burger, and you can eat them on the shore too. Mad Mary’s in Bouley Bay is very good and tends not to attract the coach tours, unlike some of the bigger ones. Bouley Bay also has a dive centre if that interests anyone. If short but fun walks are your thing, Devil’s Hole is quite eerie in the right light, and Plemont Bay is impressive at high tide if you’ve just raced up the steps! The north coast has good cliff walks if you want to shake the cobwebs.
Enjoy!