Okay, little one, let me explain what circumcellions are in a very simple way.
Circumcellions were a group of people from a long time ago who lived in North Africa. They were called that because they walked around (circum means "around" in a fancy language called Latin) the countryside doing things they thought were good.
But sometimes, these actions were not so good, and sometimes they were even dangerous. This group of people acted like they were doing good things, but sometimes they caused trouble in their communities.
They thought they were serving God and wanted to prove it by doing things like being very strict with themselves, begging for food, and getting into fights with people who didn't believe the same things they did.
So, to sum up, circumcellions were a group of people who thought they were doing good things for God, but sometimes they caused problems instead of helping. And we don't encourage behaving like that, right?