Many families join a local family based facility like a Y so that they can find activities that are not too strenuous for children but are challenging for adults. Swimming is one of the best family activities. Lessons for children with parents available for support and a lane for adult laps make for a pleasant work out for all. When everyone can swim, pool games, races, and boating trips are in order. Then the sky s the limit with all sorts of boating sports, snorkeling, diving etc.
Water sports are only one area that the family can enjoy.
Running and walking are another options. Young children may start with a mile course, but your older children will soon outpace you and certainly out distance you. In our family, tennis was the game. Our son stared at 3 years old. He would come to the court and play with balls, running after them, practice throwing, and later, practice hitting against a wall.