They won't. It happens thousands of times every kitten season all over
the country. I had four tiny
kittens left on the porch in a bucket once, and the next year had a
kitten taped up in a cardboard
box in the driveway. Someone left kittens in a plastic container
overnight at the front door of the shelter.
They weren't so lucky. It rained that night, and they drowned.

Sherry