Designate an official family photographer (or two); take lots of pictures, especially of big events. And don't forget a tripod for the group portrait. Afterward, have a photo book printed for each family.
Balboa Island Family Reunion at the beach house- Newport Beach Wedding, Newborn, and Portrait, Photographers in Orange County, Colorful Outfit Ideas, Blue, Coral, White, Beige, Polo Shirts, Summer Time, GilmoreStudios.com
Family/extended family pictures. Fun colors and idea. Wouldn't have to be beach theme but I like the idea of not trying to make the little ones sit and smile when you can catch so much more of their sweet personalities with something like this!