An atom is a tiny little thing that you can't see with your eyes, but it's what everything around you is made of. Imagine a tiny little ball that has a bunch of even tinier things buzzing around it really fast. These little things are called electrons and they circle around the ball.
In the middle of the ball, there is an even tinier thing called a nucleus. The nucleus is like the boss of the atom and it attracts the electrons with its positive charge.
The nucleus is made up of even smaller things called protons and neutrons. The protons have a positive charge and the neutrons have no charge at all.
Every atom has a different number of protons which makes it unique. Different atoms can bond together to make molecules, kind of like how different Lego blocks can stick together to make a bigger toy.
And that's what an atom is! A tiny little Lego block that makes up everything around us.