Yeah, the Keys are not known for having expansive beaches because the islands sit on top of hard coral reefs. Bahia Honda State Park is the exception, with an incredible beach, but that s quite a ride from Key Largo. Most beaches in the Keys are imported little pockets of sand. You ll find public beaches near Key Largo at John Pennekamp State Park at Mile Marker 102.5 and also at Harry Harris Park Beach at Mile Marker 92.5 (a kid-friendly beach). I believe there is a small fee at these locations. In addition, most of the major resorts around Key Largo have little private beaches too. I suppose if you don t see a private property sign, you can swim wherever you want. But beware! If you re going into the water, it would be best to wear some kind of footwear because there may be jagged coral. The last thing you need is a bloody foot.
key biscayne or miami beach, i once went to john pennekamp in key largo and got key lice the water in the keys is gross with very few exceptions. you can drive 15 minutes to the tiki bar hotel they have a beach behind but again the water is not great