DH and I stayed at the Key Largo Hilton in August. They had a pretty good deal going and they have a water-sports company onsite for parasailing, renting Waverunners, kayaks, etc. They have two pools. The resort has one of the few "beaches" in Key Largo, but they're all pretty small. Much of the Hilton's grounds is wooded and there are squirrels and lizards everywhere outside that your daughter might like.
It's on the south end of town, away from the main area and marina. That's a plus for it being quiet, a minus for needing a car to go anywhere to eat, shop, etc.
One afternoon we took a Waverunner tour (from an outside company) all around and through the mangrove islands around the Middle Keys. It was so neat. Lots of opportunities to snorkel in the area too.
I liked Key West the one time we visited but I think the Upper Keys are more family-friendly. Almost everything revolves around the water.
PHXscuba