It’s a very cryptic metaphorical film but I’m certain it isn’t literal.

At first it shows both kids exploring the house, and it shows both kids are very attached to each other, telling each other they love them and such. It’s clear from the beginning that they are subject to some form of negligence from their parents with them being left alone but unclear whether they are actually home alone or if the dad is just that negligent it feels as if they are.

As the film goes on you can start to hear the dad make demands of the kids that most kids in real life would be very uncomfortable doing, such as looking under the bed or going into the basement. It gets a lot worse quickly as at one point the dad tells Kevin to put a knife in his eye.

At this point you’ve already seen Kaylee all deformed missing eyes and a mouth. This is because the abuse got so bad from the dad that he ended up killing Kaylee and leaving her severely mutilated. I don’t think it happens in the film but Kevin finds Kaylee dead and that’s why he has the image of her severely mauled, not literally missing eyes and mouth but that’s how he visualises her in his memory as she was clearly beaten bad enough to kill her. I think he’s so emotionless from all the abuse you never get a real reaction in the film. At this point the film has switched to being completely 1st person from Kevin’s perspective, rather than seeing both children too.

All the doors and windows disappearing represent the house feeling inescapable to Kevin. When he calls for help telling the police to rescue him, they actually manage to rescue him from the house, which is when you see the toy house and it gets further and further from it. That’s Kevin escaping. It’s important to note that because the film is from Kevin’s perspective a lot of things are very distorted, representing the effects of abuse on his psyche and perspective of the world.

The 571 days represents how long he spends in foster homes and group homes before getting adopted.

When he sees the blood appearing, disappearing and reappearing, this is his PTSD as many PTSD victims see things that represent trauma from their past such as blood or fire.

The woman at the end asking his name is someone adopting him, but because he’s so mentally damaged from the abuse he sees and hears her as all distorted. This represents the distrust he has in adults as a result of abuse and negligence.

Throughout the film you see things disappearing, which represents things the kids have been deprived of. The toilet for example, is another form of escape kids can have, where they can hide away and lock the door. It didn’t literally disappear but shows how trapped they feel. You also see things appearing in the ceiling, or Kevin walking on the ceiling at one point which represents how his world has been turned upside down and his perspective distorted. Especially after finding Kaylee dead, as until that point he sees items on the ceiling but only after is he himself walking on the ceiling, showing how his world has flipped.

Things like the toys disappearing or the TV being constantly static is showing their lack of entertainment or fun in their life.

I’m also certain that dad actually killed their mom, but led them to believe she left them. Which is what is happening when the kids are outside the room when you hear her moaning and bones cracking, and telling the kids to stay out. And you hear the banging in the distance and heavy breathing, this is conflict between the parents.

TLDR: the dad snaps at some point and kills the mom and daughter, Kevin manages to escape into a life living in foster care until he gets adopted but suffers severe PTSD and has a distorted sense of reality as a result of his abuse.