Okay kiddo, so imagine you're playing with a group of friends and one friend keeps doing something that's not allowed. Maybe they're cheating or not following the rules of the game. The other friends might decide to ban them from playing because they're not playing fair.
That's kind of what happened with Croatia. They were a country playing by a set of rules with other countries in an organization called the EU. But the EU thought that Croatia wasn't following the rules very well, and wasn't doing things in the right way.
So, the EU decided to ban Croatia from some of the fun things that they get to do when they follow the rules. This includes being able to make some types of deals with other countries in the EU.
Now, Croatia can still be a part of the EU and still do some of the important things, but they might have to follow some more strict rules and restrictions until they can prove that they can play fair with the other countries.