Spoilers ahead.
If you have any knowledge of movies you're going to guess the twist very early in. It's so obvious, in my opinion, that you might think it's a fake out twist for an even bigger twist. But no, one of the kids has been dead the whole time.
Having that in knowledge, it makes a good chunk of the film fall apart. It's believeable that two mentally unwell kids could overpower their mom, tie her to a bed,…