Getting Schooled

I think sometimes it is easy to underestimate the cleverness of preschoolers. On my brake I happen to overhear a substitute teacher managing a group of preschoolers.
"Okay, kids!" He began, "I would like to hear about how smart you are."
"Yeaaaaaaa-h!" They cheered.
"I am so glad." He laughed.

The room went silent with the exception of a few giggles.
"So children, why do you think birds fly south for the winter?"
"I know, I know!" Chimed through the room.

"Hillary, tell us what you think the answer is."
"It's a-cause birdies don't like to walk!"

The teacher hesitated, then said, "That's true! Let's clap for Hillary!"