At the beginning of the film where Kate and Alex are in bed, the time on the alarm clock is 11:20. They talk for about 20 seconds and when the angle shows the alarm clock again, the time is 12:04.
When Kate and Alex are hauling the suitcase out to their car its bulging throughout the scene as if its over stuffed. When we see the shot of the suitcase in the lake the suitcase is not bulging and appears to be empty.
(at around 49 mins) When they all pull up to their friends place, and the camera switches to a 45 degree overhead shot, on the right side of the screen around half way up you can see a foot disappear then a lower half of someones leg appear in the garden.
The entire movie Kate realizes how secretive she needs to be about getting medication, yet when she gets the last remaining doses she leaves the building yelling into her cell phone about it.
Since all returned people have to be in the detention camps and government agents are checking addresses for those who have not reported, there's no way that the boy from the beginning of the film could be outside the hospital with his parents.
At the beginning, Kate explains to the parents of the returned child to wear gloves if he happens to bleed. In the end, Alex bleeds on his mouth, coughs blood in his hand with which he then takes gun to give it to Kate, with her additionally hugging him without any protection.