Most sight casting tarpon flats are set aside for flyfishermen only. Yes, as long as the child is over 8 years old. Bear in mind that you will be stalking very spooky fish in very shallow water, and must be quiet. This is impossible to answer. Fishing in the Keys is always challenging, even for experienced anglers.
Successful anglers practice casting into, across, and downwind before arriving.
Anglers have a choice of flying into either Miami or Ft. Lauderdale airports, with travel time to the Keys only about 30 minutes different, between them. A rental car is the easiest mode of transport, however,shuttles are available from the airports. If you opt for a shuttle, keep in mind there is no public transportation in the Keys and cab fare is expensive. The Florida Turnpike runs just west of both Miami and Ft.