This all happened in Holland a long time ago""--but given the paucity of vicarious picture-book adventures, the energetic doings of eleven-year-old Jan Jansen, his little sister Annette, and his friend Will could be a welcome dash of the old Hans Brinker/child buccaneer spirit. Jan's fisherman-father is dead, and to help out he wants to go fishing with the men. ""Why don't you fish from the jolly boat?"" one of them teases. And so, at Will's suggestion, the two boys fit the small, round-bottomed craft with a mast and a sail, and set out--Annette, at her insistence, going along too. But when they've caught a few fish and turn toward home, the rising wind tears the sail loose, and for two days the boat is tossed about in the stormy sea. Then the children, asleep, are rescued by a passing ship--and the best part of the story begins. They're carried in triumph to Amsterdam; tour the city's canals in the jolly boat (an irresistible double-spread of stepped gables, domestic-and-trade bustle, and gesticulating local types); and head for their island home--overland. An accommodating waggoner carries the boat--until the wagon breaks down on the muddy road. An old man asks them if they're ""waiting . . . for the Flood""--and gives them some staves to roll the boat on. The water rises, floating the boat; using the staves as poles, they push it into a small canal; taking a cue from a fox, they steal some food (later, they'll confess and make recompense); and, in sight of their island, go aground. But all ends as it should, with their parents' joyful relief and permission for Jan to fish with the men. The full-color pictures capture the excitement, humor, and discouragement--and give an old-fashioned storybook flavor to the setting. It's in no way distinguished, but it is good, lively fun.