Hi Chiara,
As an American, your question seems strange to me, as I can think of a thousand places you can go by surface transport. Without knowing your tastes and temperment for exotic places, (and keeping in mind the difficulties of travelling with children), I would recommend renting a holiday camper in France or Italy, charter a sailboat in the Greek Isles (you must pass a sailing certification course for this, but it's quite inexpensive, and fun), or for a really adventurous trip, go by train or ship to St. Petersburg, Russia.