Details of a Greyhound hop from Chicago to Yellowstone Park are enumerated in a friendly family story that seems to make bussing more attractive than it actually is. But perhaps it is -- for children. When the time comes for their father's summer vacation, Ned and Nancy are ecstatic over plans for the bus trip and camping expedition the family undertakes in the park. And, none the worse for wear, they enjoy the return trip as much as the first. Would all youngsters were as eager and well behaved as they!