Okay kiddo, imagine the sky is like a big pool of water. Sometimes, the pool gets really warm and starts to make big bubbles. Those bubbles grow and grow until they burst and make a big splash. That's kind of like what happens with a downburst!
Basically, a downburst is when really warm air high in the sky suddenly falls down to the ground really fast. When the warm air hits the ground, it gets all squished up and has nowhere to go but out in all directions. This can create a really strong wind called a downdraft that can knock things over, like trees or even buildings! It's kind of like a giant gust of wind that comes out of nowhere.
Sometimes, downbursts can happen during thunderstorms when there are really strong winds up high in the clouds. The winds can mix together like a bunch of swirling spaghetti and make a downburst when they come down to the ground. But don't worry, downbursts don't happen all the time and when they do, they usually don't last very long!