Okay kiddo, so imagine there was a time long ago when a group of people in a country called Germany thought that some groups of people were not as important as others. They thought that some people were weaker or had traits they didn't like. This was called discrimination, which means treating someone differently because of something that they can't control like their race, religion, or disability.
The German government created something called "Action T4" which was a plan to remove people with disabilities from society. They did this by forced sterilization, taking children away from their families, and eventually killing them in special places called "euthanasia centers". This was very cruel and unfair to the people affected by it.
The people in charge of "Action T4" thought they were doing the right thing, but history has shown us that what they did was wrong and hurtful. Today, we try to treat everyone equally and make sure that everyone has the same rights and opportunities, no matter what their differences are.