The name Mary Poppins may be enough to elicit wild cheers from the most jaded of book buyers, but this is not another rollicking adventure with the classic heroine. Instead it recounts 26 short episodes about Mary and her brood, each one emphasizing one letter of the alphabet, throughout. For example: ""I is for In. Inside. Indoors. In a middle. In a temper. That's where the children are today, because It Is raining."" How Mary handles the situation is the subject here. Mary Shepard's whimsical drawings on deep yellow or blue ground are Poppins to perfection. Children who already know their ABCs will find the tongue twisting a challenge and the little stories an excellent aperitif (or a dessert) to the original world of mary Poppins.