Okay kiddo, so a long time ago in Poland, there were some people called Jews. They were just like anyone else, but some people didn't like them just because they were Jewish. This is called prejudice or discrimination, and it's not nice at all.
During a really bad time in history called World War II, some very powerful and scary people called Nazis took over Poland and other countries. They didn't like Jews either, and they did some really horrible things to them, like hurting them and taking away their homes.
After the war ended, Poland was a mess, and people were trying to figure out what to do next. But some people still didn't like Jews, and they started to hurt them again. This is called anti-Semitic violence.
It's like someone picking on you just because you have brown hair or wear glasses. It's not fair or right, and it's very mean and hurtful. Unfortunately, some people still act this way even today, and we need to be kind and stand up for what's right when we see it happening.