9. Big (1988)
We all probably remember the iconic FAO Schwartz piano-playing/dancing scene in Big, but the rest of the movie is sort of ingenious. Although the whole younger person/older person switch movie has been done tons of times, Big is the best example of how this formula works.
A slightly creepier version with an awkward actor like Michael Cera playing Tom Hanks’ character would be a fun way to play up Cera’s sheepish and perpetual childlike quality.