Original illustrations by DyAnne DiSalvo, though my copy is a re-release with illustrations redone by Carol Thompson.
I have this story in Two Times the Fun, a collection of the Janet and Jimmy stories. Janet and Jimmy's mother thinks they've outgrown their shoes, so they all go on an adventure to the shoe store.
Janet and Jimmy are excited to get something new. They can't wait to surprise their friend, the mailman, with new shoes. But the salesman measures their feet and finds the twins don't need new shoes after all. How can they surprise the mailman now?