Daniel Stern, who played Marv in the first two films, was approached to reprise his role in this one. Stern quickly declined, calling it "an insult, total garbage." On the other hand, Joe Pesci wasn't offered to reprise his role as Harry. Instead, Harry's name was only mentioned.
The producers had hoped that this movie would lead to a Home Alone TV series, and several of the main cast members had clauses in their contracts that would have bought them back for such a series. This movie failed to perform up to expectations in the ratings, though, and the series never went ahead.
The trivia items below may give away important plot points.
In the original ending, Kevin's parents did not get back together. His father stayed with Natalie, and his mother started dating a police officer who turned out to be Marv's younger, more honest brother. This was changed when the producers decided they wanted the film to set up a TV series, and so Kevin's parents did get back together at the end, while the police officer was deleted altogether from the script.