Why do they SLEEP?

My child sleeps at the jeepney when we are on the way to SM. She sleeps also in the taxi when we are on our way home. Why do children sleep when they travel?

Obviously, we also sleep sometimes when we are in the bus or in the car when we travel in distance places. I remember when I was child I do sleep in the jeepney too..LOL!!! may pinagmanahan pala si Kyla.

I'm so tired holding her head because she sleeps in the jeepney but when she saw the shopping mall. She hurriedly opens her eyes wide.
She is amazing!