First of all, the time travel cosmology made no damned sense. When they wind it back, the house and grounds reset to an earlier configuration (thus, no bomb) and presumably the physical bodies of the kids also reset, which is why they don't age. But it doesn't wind back their physical position, or their memories.
So that means that these aren't kids, these are shut-ins in their mid 60s trapped in kids' bodies during their Groundhog Day horror story, a few of whom are trapped in the endless nightmare of puberty.
But it does wind back the position and memories of squirrels.
Who drew the chalk outline of the Supervamp on the lawn, and more importantly when? Why didn't that reset? For that scene to make sense it... well, it.. no, there's just no way to make that scene make sense. Auugh!
Also: they can communicate with the outside world. The phone works, they can walk down to the pub. And the past can affect the future: the house doesn't exist in a slow-time bubble of 1940 that exists in 2016, it is literally still 1940. And they don't think to make a call or send a telegram to prevent the death of Kindly Hitman Grampa? They can try as many times as they want until they get it right!
So then they finally save Kindly Hitman Grampa (ooh, spoilers) which leaves the kid with no justification for having left the US in the first place. And what ridiculous mess was left behind in Grampa's memories, anyway? You have to explain these things.
In short, this movie sucked.
Fucking time travel.
It could have just been about Zalgo Babies fighting Supervamps or whatever, but they had to go and rub time travel all over it too.