Okay kiddo, imagine you and your friends have a club, and you're all in charge of making decisions for the club together. But one day, your friend who is the leader of the club decides to get rid of some of the other members without telling anyone.
The night of the long knives was kind of like that. It happened a long time ago in Germany, in 1934. At the time, there was a guy named Adolf Hitler who was the leader of Germany, and he had a group of people who helped him lead the country. They were called the Nazi party.
One night, Hitler decided he didn't like some of his friends in the Nazi party anymore, so he secretly told some of his helpers to go and arrest them. They did it really quickly and quietly, while everyone was sleeping. They arrested some of Hitler's friends, and some other people who weren't even in the Nazi party but Hitler didn't like them for some reason.
These people who were arrested were the victims of the night of the long knives. They were either killed or put in jail, and it was all because Hitler decided he didn't like them anymore.
It was really unfair, because these people thought they were part of the club and that they were working together with Hitler to make Germany better. But Hitler didn't care about that. He just wanted to be in charge and get rid of anyone who stood in his way.
So, the night of the long knives was a really sad and scary time for the people who were victims of it. It was a reminder that sometimes, people who we think are our friends can turn on us and hurt us really badly.