Young children have this wonderful and at times incredibly frustrating ability to completely ignore the past, even moments ago, and pay no heed whatsoever to the future. They're a fabulous lesson in living in the present. That they were miserable just now when someone took what they were playing with — doesn't matter any more. That playing in the puddle for longer means you'll miss the bus, and be late for lunch with friends — doesn't matter. All that matters is now.
I have a theory that as we grow older our circle of attention expands.