Sit on the floor and play with their toys.
Then take a nap.
Repeat.
Then take a nap.
Repeat.
My son's favorite was "The wolf book" aka, The Three Little Pigs. That I could recite...with the voices. I remember doing so as last ditch entertainment as we neared home after a ten hour drive. He was sick, hungry and tired.
They are only so little for a brief time.