It depends especially on the level of comfort and facilities on board you are looking for:
First, you must get to Ecuador Mainland. Make sure you arrive to Quito or Guayaquil at least one day before your departure to the Galapagos; there are no direct connections with international flights and flights to Galapagos Islands depart from mainland Ecuador early in the morning from Quito and/or Guayaquil.
Visitors arrive by plane from Mainland (flight takes about 2 ½ hours) with three main Airlines: AVIANCA, LAN and TAME and arrive to Galapagos to one of its two Airports: One in Baltra Island and one in San Cristobal.
Some cruises do not allow small children on board, mainly for safety reasons as small yachts/catamarans have many open spaces and steep stairs that are not suitable for children to run around. Other cruises, especially the large vessels do accept small children on board and even have qualified guides and staff on board to make a magical experience for small children.
Most yachts/catamarans accept children over 8 years-old on board and offer special rates to children up to 11 years-old for cruises and flights as per availability and feasibility to accommodate a Family on board; with all cruises, it is required as pre-requisite to have parents sign a release form if travelling with children.
On a general basis, unless included on the given price for the confirmed cruise, passenger needs to bring enough cash on board to cover costs like Galapagos entrance fee ($100 p.p. in cash on arrival to Islands), mandatory Transit Control Card ($20 p.p. paid before check-in in cash), snorkeling equipment & wet suit rental (in cash on board), personal expenses, extras, soft & alcoholic drinks, tips for guide& crew and other expenses not specified in the itinerary.
Some Luxury and First accept Credit Card payments on board for on board consumption but Midrange and Economy require payments in cash only. It is imperative that you bring enough cash (U.S. Dollars) in all cases to cover your expenses while cruising the Galapagos.