Here are some things to keep in mind:
* The mother cat may not always bring food to her kittens. If she is unable to find food, she may have to leave her kittens for longer periods of time.
* The mother cat may also leave her kittens to use the litter box or to stretch her legs.
* If the mother cat is gone for more than a few hours, you may want to check on her kittens to make sure they are okay.
As long as the kittens are eating and drinking and appear to be healthy, you do not need to worry about the mother cat leaving them for a few hours.