Okay kiddo, so the archdiocese of Mechelen-Brussels is a big group of Catholic churches in a place called Belgium. Think of it like a big family of churches that work together under one leader, called an archbishop. This archbishop is like the boss of the churches and helps make important decisions for all the people who go to these churches.
These churches have been there for a very long time, since the olden days when people used to pray in fancy buildings called cathedrals. They have lots of different jobs, like helping people who are sick or poor, and teaching people about God and religion.
Sometimes, the archdiocese of Mechelen-Brussels makes news because it's a big group with lots of members and people might want to know what they are doing. But at the end of the day, they are just a group of churches who want to help people and follow their faith.