My family of five (3 kids age 9,7,3) will be at Hawks Cay (middle Keys) in March.

Would like recommendations on local eateries (Fun, Not too expensive, Not to far).

Also any suggestions for activities would be appreciated

Two fun activities:

1) the beach at Bahia Hondo State Park.
2) snorkeling at Pennekamp Coral State Park.

The latter specializes in helping neophyte snorkelers, but does require that people be able to swim. I'm not certain about age requirements.

Hawk's Cay is fairly isolated. I normally recommend it to families with very young children because I've heard the children's programs are good.

Both Bahia Honda and Pennekamp National Park are great ideas, but Bahia Honda is about 25 miles from Hawk's Cay, and Key Largo (the location of Pennekamp) is nearly 40 miles away. Under normal circumstances that wouldn't see too far, but driving through the keys can be extremely slow, as it's mostly a 2-lane highway.

The Turtle Hospital in Marathon is worth a visit. They do a fascinating job there, and it's well-worth a look.
http://www.turtlehospital.org/

The Florida Keys Wild Bird rehab site is also a great stop! It's closer to Key Largo, and you get up-close and personal to the birds, both inside and outside the cages. http://www.fkwbc.org/

The Dolphin Research center in Marathon would be fun for kids and adults. We spent several hours there.

There is a restaurant called the Island Tiki Bar before you enter Marathon. You eat outside, good food, casual and you can feed the fish under the dock. The kids would love it. Warning though it is very crowded on the weekends.

There is also Robbies where you feed the tarpon. The fish are enormous and go absolutely nuts! You can also get good (cheap) trinkets here for the kids. I can't remember exactly where it is though. I think between Islamorada and Marathon on the gulf side.

Robbies is at Mile Marker (MM) 77

robbies.com

Marathon Lady in Marathon is a great 1/2 of fishing. It's a large excursion boat..they supply the poles, bait and ake the fish off the hooks for you and fillet your catch for a small fee on the dock when you arrive. You can choose between AM and PM and I think they do night fishing also but we've never done that. We've been visiting Marathon about yearly for 40 years..you'll love the Keys! And, the Island Tiki Bar mentioned above is great. It's at MM54, Bayside. Theater of the Sea in Islamorada is fun with kids also...guided marine life tours; dolphins and sea lion shows also. www.theaterofthesea.com Have fun!