Kenneth Beatty  age 5; of Ottawa  Canada:

What makes an echo?

At five  young Kenneth is old enough to bounce a ball.. Since he has wondered about echos he has also noticed how a ball bounces. You throw its it hits something hardy turns around and cames back part way back. An echo also acts something like that.

You throw your voice out into the air every time you speak. The sound goes on and on through the air. It gets dimmer arid dimmer until it finally fades away. But once in a great while it hits something hard and solid. This may be a wall a canyon or a steep cliff.

If the sound isn’t too tired by then  it turns around and comes back again. Like the ball it bounces. If you are a short way from that steep cliffs the sound comes back quickly maybe before you have finished crying Helos If you are a longer way from the cliffs the echo is longer before it comes back. For it takes time for sound to travel  bounce and came back in an echo roll.