Tell your child that the atom is the smallest particle of an element. An element is a substance that is in its simplest form and cannot be broken down further. Some examples of elements include: Hydrogen, Oxygen, Iron, Silver, Gold, etc..
Tell your child that inside of the atom there is a nucleus. The center part of the atom. Inside of the nucleus are the protons and neutrons. Protons are the positively charged particles of the atom and the neutrons are neutral. They do not have a charge.
Tell your child that the nucleus is surrounded by negatively charged particles called electrons. These particles move rapidly around the nucleus.
Electrons flow in invisible orbitals. Based on the number of electrons left in the outermost orbitals determines how the atom bonds.