In the movie Vacancy, How did Amy and David's son Charlie die?

Question

In the movie Vacancy, How did Amy and David's son Charlie die?

During the movie, Amy starts crying and saying to David something about being sorry about Charlie, sorry for leaving the gate open or letting him near the..? Something? Didn't catch that part because she was a little hard to understand. Help, anyone?

Answer 1

It is never indicated, only alluded to that it was while Amy was caring for Charlie, which is why she feels so much guilt and on anti-anxiety medications.