McPhail can make you uneasy with the spectacle of fat Pig Pig, who is well past babyhood but still insists on sleeping in a crib, eating Pablum in a high chair, being pushed in a stroller, and throwing tantrums in the super market. His precipitous leap into maturity occurs when his mother, exhausted from pushing the oversized load, loses hold of his stroller--which then zooms downhill toward a parked carriage containing a real baby. Well, ""Pig Pig whirled into action,"" stopping the stroller in time to save the baby. Praised for his bravery by assorted onlookers, Pig Pig then insists on pushing his tired mother home in the stroller. This might hold whatever attention the 500 words and background-free pictures demand, but whether viewed as comedy or therapy or some nebulous blend of the two, the story suffers from developmental problems of its own--as well as from a want of inspiration. Anyone drawn in by the probem will be let down by the snap solution.