Vice Versa

Vice Versa is a 1988 film starring Judge Reinhold, Fred Savage and Swoosie Kurtz. It's a body-swap comedy revolving around a thirty-ish department store executive named Marshall Seymour and his preteen son Charlie. It's mixed with a caper/MacGuffin plot involving a mysterious jeweled skull which Marshall accidentally acquires, and which is now being hunted by two crooks. The two plots are joined because when two people touch the skull and say the right words, it can make people grow up, shrink or change sexes to resemble each other.

This being set in the Eighties, the family drama involves materialism and divorce. Marshall is estranged from Charlie's mother and has thrown himself into his career in retail management. He seems to like the lifestyle of expensive holidays and designer suits and he also has a killer bod. Charlie is small for his age and gets bullied by older/bigger boys.

One morning, as they get ready for the day, Charlie and Marshall have an argument about their lives. This leads to them both wishing to change places with each other, unfortunately while touching the mysterious crystal skull. The room fills with eerie light as Marshall gets smaller and smaller and Charlie goes through a full growth spurt in seconds, leaving them looking like exact duplicates of each other.

Half the film involves their attempts to live each other's lives whilst waiting to fix the change, so 'Charlie' (Marshall) goes to school whilst 'Marshall' Charlie goes to work. The other half involves the attempts of a couple of crooks to steal the skull back.

Based on a novel of the same name by F. Antsey.

Tropes used in Vice Versa include:

An Aesop: Along the lines of "be thankful with what you've got".
Be Careful What You Wish For: If you don't want to find yourself either miniaturized or suddenly thrust into an adult world for which you've had no preparation.
Fountain of Youth: 6'2" father Marshall is reduced to a small-for-his age preteen.
Freaky Friday Flip: Here, the bodies change rather than the minds moving from one body to another. But the outcome is the same -- after a change of clothes.
Genre Savvy: At the end, as they prepare to reverse the swap, Charlie (as an adult) instructs his child-sized father to remove his PJs to prevent them being shredded to bits in the ensuing transformation.
Karmic Transformation: The father is forced to remember how a child's life feels, and the female crook takes on the form of the male minion she abused.
McGuffin: Ownership of the skull drives the subplot and Failure Is the Only Option keeps the man in a child's body and the child in a man's body until the lesson is learned.
Only Works Once: In the novel. In the movie, they need to work out how they did it, then they can do it again.
Overnight Age-Up: Wide eyed preteen Charlie has to deal with the corporate world.