Although a tux is always appropriate, a suit is generally what one sees the most of these days and this is what I wear. I no longer bring my tuxedo for cruises from the U.S. Actually a jacket and tie will be fine.
Cocktail dresses are popular with the ladies. As for kids - anything "nice" will do. Maybe pants and a button down shirt for the boy. A tie and jacket if he'll put up with it. It is quite common to see teenage girls dressed up and looking very grown up in many cases - but any nice dress will be fine.