My hubby and I were there last June and it was hot during the day. Fortunately, we were at the Hilton resort and the pool area is wonderful. Full service pool bar/grill and good shady spaces to lay out. When we were there, the beaches were not all that great. In fact, we were told by many locals to not get in the water because of how dirty/toxic it was. Many will tell you to take snorkeling trips out to the reefs to experience the true blue waters that you are wanting. We took a trip out to Fort Jefferson and had a fantastic time. There are a couple of small beach areas there and we saw quite a few colorful fish. If you're just wanting to lay out - the Hilton is top notch. Close to everything and right off of Mallory Square. Be sure to eat breakfast at Ricky's Blue Heaven. Outdoor eating at its finest with the wild Key West chickens wandering around the grounds. The food was excellent and your kids will be very entertained.