Being a few minutes late from lunch is a bit of an extreme reason to be fired. However, in an interview you can state you were late coming back from lunch. If you feel it's appropriate, elaborate and state you received a call from your child's daycare about a family matter. Usually that's the best way to go. I wouldn't mention the sleeping part, unless, of course, your previous job knew about that and will tell this prospective employer. Otherwise, state you won't do it again.