On the girl's trip to the cave with the boys, her skirt is red. However, when she's walking along the tree it's brown. After that scene, it changes back to red for the rest of that trip.
When Tuur fight with Lambert his shirt is open , however, when he walks away it is buttoned up. When he starts cycling it is open again.
During the Occupation of The Netherlands (1940-1945) two boys find an American comic book, presumably left by a downed American pilot. This comic book, a dangerous item in those days, reappears in scenes that follow, until one of the boys' mother confiscates and burns it. The magazine that ends up in the stove is a 1952 reprint, which follows from the cover design (Classics Illustrated instead of Classic Comics) and the cover price (15c instead of the regular '40's price of 10c.).