Joe Pesci, who ended up portraying Harry, wasn’t used to acting in a family-friendly movie, and reportedly cursed often on set.
Columbus, who’d wanted to hire Pesci based on his roles in R-rated films like Raging Bull and Goodfellas, advised Pesci to say “fridge” instead of “fuck”. Columbus also noted in the director’s commentary that Pesci wasn’t always thrilled to be on a set where a child was the star of the movie.