My DH has done CC fishing and really enjoyed it. It is pricey, but there are only 6 or 8 people on the boat, so you get a lot of individual help. The Key West charter linked here sounds like what we call a "head boat", basically a set price per head. There can be up to 50 people on these boats. It's a relatively inexpensive way to get out into the water to fish, but you might not catch a lot. We've done this a few times here where we live, and as long as there's an adult along to help the kids, you can do okay. Just don't expect it to be a fishing charter like you see on ESPN outdoors. The CC experience is like the ESPN outdoors charters.
One thing I wouldn't do again (cause we did it) was ask for a fishing charter in Cozumel. When you are ashore in Cozumel is primarily during the heat of the day, and the fishing just isn't very good. We spent a lot of money for our family to go out on a pretty shabby boat with no bathroom facilities, only 4 poles, and we caught absolutely nothing. The crew didn't speak English, so they just didn't understand when we said it would be okay to go somewhere else. They took us to where you can catch the really big fish, but when they weren't biting, we just wanted to go somewhere that we could catch anything. Finally we were able to convince them just to return to shore.