Summer Switch

"A boy and his father literally find themselves in each other's shoes." --summary, library records of the 1st ed. The little brother and father of Annabel Andrews are in each other's bodies (they "switch bodies"), as happened to Annabel and her mother in the first book, Freaky Friday. Thus either novel "may be considered a modern retelling of Vice Versa, the 1882 novel by F. Anstey, in which the protagonists are a father and son." --Wikipedia