I agree that on the Pacific side the viz can be terrible at times and
often there are too many high waves. But, on the Atlantic side things
are quite different. Try around Puerto Viego and Punta Ulva, there are
some really nice beaches with rocky outcrops that are perfect for
snorkeling. And the water is quite warm. A ferry used to run from Puerto
Viego to Boca del Torres in Panama, but I think that has now been
discontinued. Remember this is just a couple of miles north of the
Panamanian border. This part of Costa Rica is mostly visited by
Europeans (Dutch, Belgians, French, Italians etc) and there are some
great little hotels tucked away on some remote beaches. But wherever you
end up I hope you and the kids have a great time. Enjoy.
William.