The Martin kids, Elizabeth, Jeremy, and Harry, are tired of their strict and overbearing mother, Mrs. Martin. One day they come across a book of spells and discover the "mommy market" spell. They recite the spell and find themselves in a mysterious marketplace where they can trade in their current mother for a new one.
They try out a few different mothers, including a fun-loving and carefree "Slippery-Foot Mama," a nurturing and patient "Cookie Mama," and a sophisticated and elegant "Working Mama." However, they quickly realize that no mother is perfect and they miss their own.
When they try to return to the mommy market to retrieve their original mother, they discover that they are unable to reverse the spell. They must find another way to get their real mother back.
Through a series of adventures and challenges, the Martin kids learn to appreciate their mother for who she is and come to understand the importance of family and love. In the end, they finally find a way to break the spell and reunite with their original mother, bringing the message home that no one can replace the love and bond of a real family.