A very Similar movie
Somewhere I've read a synopsis or brief review of a movie that's very much like this, only the secluded valley is populated only by children. There's still the mutants (or what not) on the outside just like in this one.
Does this ring a bell with anyone?
(I'm pretty sure it was a movie but it could have been a book, but I don't think so. Any help will be appreciated.)
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"Molly ... there's a dog. So pretty ... how he shines."