Everything we see is made up of tiny little parts called atoms. The atoms are made of even smaller parts. These are called protons, electrons and neutrons.
Protons have a positive (+) charge. Electrons have a negative (-) charge. Neutrons have no charge. Usually, atoms have the same number of electrons and protons. Then the atom has no charge, it is "neutral.
If you rub things together, electrons can move from one atom to another. Some atoms get extra electrons. They have a negative charge. Other atoms lose electrons. They have a positive charge.
When charges are separated like this, it is called static electricity.
Watch the pictures of the children working on static electricity