When Michiel shoots Oom Ben in the woods, the hammer of the pistol goes from the fully cocked position before the shot, to a semi-cocked position after the shot. The action of the pistol should have cocked the hammer all the way back. Almost to the web of Michiel's hand.
A couple of the German vehicles bear the divisional signs of Panzer-Grenadier Division "Grossdeutschland" (a German helmet) and 2. Panzer-Division (a trident). Neither of those divisions were anywhere near the Netherlands during the winter of 1943-44.
There's a lot of snow in Oorlogswinter - except on the roofs of buildings.
When the boy gets home and opens the back door you can see the strips double layered isolation window glass.
When the boy opens the suitcase in the attic, he pulls out a Browning HighPower pistol with Pachmayr Signature rubber grips. The grips would be wood or hard plastic. Pachmayr grips would be made in the United States post WWII.
When Michiel is cycling through the village, he passes a row of houses typical for the post-war resurrection era.
When Jack and Erica are walking over the bridge near the end of the film, they are actually walking to the wrong side of the river. The wooden pylons in the water are on the side of the Veluwe, the woods in which Jack's plane crashed. Jack wanted to go to Zwolle, which is on the side Michiel is watching Jack and his sister cross the bridge. This is due to the fact that another bridge for a highway had been built next to it, which would have ended up in the movie had they filmed the right way around.