Ok kiddo, Imagine you have a toy army of robots. You can give these robots commands like "walk forward", "turn left", "turn right" and so on. And imagine you have a special remote control that can control all of these robots at once.
Now imagine someone else has a toy army of robots just like yours, but they want to use these robots to do bad things like steal information from computers or make websites crash.
To do this, they can take control of your toy army of robots without you knowing. They can do this by hacking into the toys and changing their controls so that they all listen to the bad guys' commands instead of yours.
When this happens, a group of hacked toys controlled by bad guys is called a "botnet." The bad guys can use the botnet to do bad things online without getting caught because the actions are coming from lots of different toys, not just one person.
So remember, it's important to keep your toy army safe and secure so that bad guys can't use it for their own mischievous purposes. Maybe put a password on your remote control to keep it safe!