Since the real sisters and their friends are protected by Canadian law and their information is sealed, there was no way of knowing who they were as people. Director Stan Brooks then made everyone in the young cast go home and write an essay about their character - what their favorite music was, their favorite food, and so on. Zoe Belkin wrote that Ashley is anorexic, doesn't eat and has body issues. If you watch the movie there's a cafeteria scene were she chooses Jell-O and the entire meal cuts out but she never eats any.
Georgie Henley admitted that she is terrible at riding a bike and for one scene she had to ride what she described as a "huge bike". She practiced up and down a road for 15 minutes before shooting the scene. Director Stan Brooks said in an interview that during one take he asked her to look back at her co-star Jeffrey Ballard as she rode away, which made her veer into a telephone pole.
Georgie Henley and Abigail Breslin both had to speak Dutch two times in the movie, they even had a Dutch woman on set to help them. Henley stated that she was really awful at speaking Dutch and that she at sometimes was just mumbling gibberish.
The home video sequence in the beginning of the movie is actually a real home video of Rachel and Laura Henley, Georgie Henley's sisters.
Jeffrey Ballard lost a lot of weight for the role of Justin. The idea was to show that Justin was neglected by his parents, that he's always out with his friends drinking or smoking, that he's not eating healthy. Ballard even stopped sleeping just so that he could get into Justin mindset and being disoriented.