Christopher looks as though he has a fresh haircut throughout the two year stay in the attic, while the other children have visible growth.
At the beginning "Cathy was here" is chalked on the wall, but when Cathy actually writes it on the wall, the handwriting is completely different.
When Christopher cuts Cathy's hair because there is tar in it, the tar magically disappears when Cathy asks if he thinks she's pretty, then reappears as he continues to cut.
There is a scene where Christopher has to cut Cathy's hair because it was covered in tar. In the following scenes Cathy is shown with Christopher's badly cut hairstyle. But during the entire time, Christopher's hair is styled perfectly, never needing to be cut, always perfect.
When the teens count the money they stole, a new 5 dollar bill is used.
The exterior of Foxworth Hall is obviously CGI and looks nothing like how it is described in the novels. The interiors are also noticeably small, including the attic, which is supposed to be enormous.
When Corrine brings a box of toys to the kids in the attic (after sailing), a Simon electronic game box is clearly visible in the wooden box.
Many of the fashions worn and phrases said in the film were never around in the 1950's. The girls' dresses were made by a 21st century company and were not a style worn in the 50's. Phrases like "just drop it", "you guys" and "no way" weren't used in the 1950's, either. These phrases originated from the Eighties.
Except for the rooftop sequence where Cathy tells Chris she realizes they've been locked away in Foxworth Hall for an entire year, no effort was made to make the children look weak or sunlight-deprived, even though they were supposedly locked away for over two years.
Cathy and Christopher are shown developing the habit of climbing out the attic window and sitting on the slope of the roof, looking out on the Foxworth property. During the day. They'd have been in full view of the servants or anybody else approaching the manor, the groundskeeper, for instance. They were hidden away and supposed to be a secret.
The film never mentions Christopher's ambition to be a doctor, an important part of his character (which is a major theme in the novels as well as the other Lifetime movies in the series), which was a key factor that helped the children during their imprisonment.