Based on a book by Astrid Lindgren, author of "Pippi Longstocking". Lindgren wrote the book after she saw a lonely boy sitting on a park bench in Stockholm. She wondered what he was doing there, who he was and where he would end up and that gave birth to the story of Prince Mio. The bench that the boy sat on can still be found in Stockholm today, marked with a sign saying "Mio sat here".
The Chernobyl power plant disaster occurred when the film was being shot. The crew evacuated the area completely but came back to shoot the next month. They had numerous Geiger counters set throughout the shoot to monitor radiation levels.