This is another one of those movies that could have been great. The basic premise is good - immortal cat people who kill to live, etc. - sort of a variation on the vampire concept.
The thing that makes it all fall apart is the total recklessness of the main characters. Even sociopaths know that you need to keep a low profile if you want to survive - look how long it took to catch the Unibomber, and that was because a family member figured it out.
By contrast, the kid (and to a lesser extent, the mom) behave as though they're untouchable. The kid kills without a thought for not leaving evidence or a trail or a living witness. How these people managed to stay alive and undiscovered for a month is unbelievable, let alone decades or centuries.
It's really a shame - this could have been so much more if it had been written plausibly, i.e., giving the main characters the level of common sense they would have needed to get by for so long.
Other than that, not a bad showing. I loved the bit at the end where every cat in town converges on the house - every time I put out food on the porch and see our cats suddenly rush in from wherever they were before, I think of that scene.