When Darrin and Samantha are parked on the street and Sam changes him back to a boy, they're parked in front of the "Oriental Shop." Then, Darrin, the boy, races across the street and meets the two other boys in front of the same "Oriental Shop."
Although it's been stated several times that a witch cannot undo another witch's spell, Samantha manages to undo Endora's spell and change Darrin back to adulthood in the phone booth.