Factual error: When Tom has decided his scout group will have to go for the food and then his look for his son later, they are stood on a green. There is a war memorial dedicated to both World Wars, 1914 - 1918 and 1939 - 1945. That's got to be in Canada, as the USA didn't enter either war until later than those dates. (00:28:00)
Character mistake: Tom Mason makes references to smaller armies defeating larger ones, of which history is rife with examples. He cites the Scottish defeating 'the British' at the Battle of Stirling Bridge. 'The British' did not exist at that time. The Scots administered a beating against the English in the Scottish War of Independence, against the Earl of Surrey, under Edward I. Someone with his level of knowledge would know that.
Continuity mistake: When Tom starts shooting at the skitter in the food depot, the shots from his gun, the hits on the metal, and sound of ricochet are inconsistent with each other.