Crystal Cruises isn’t shy about doling out incentives, and families looking for a high-end cruise experience in Europe this summer will be pleased with a recently announced promotion. Crystal invites kids 17 and under to cruise for free on two Crystal Symphony Europe cruises this summer, when sailing in a third berth with two full-fare adults (families of four with two children would have to book two cabins – the ship has 10 connecting staterooms and 89 staterooms with a third berth).