Explain the Big Bang Theory to kids using simple terminology and metaphors they can understand to help them relate the new concepts to concepts they already know. For example, remind them that one year is the amount of time it takes to get from one birthday to the next to help them understand just how long ago it was 14 billion years ago, when scientists believed the big bang occurred.
Describe to children that scientists believe the entire universe was contained inside a very hot bubble much smaller than the tip of a needle, so they can imagine how the universe must have been ready to burst out of that extremely tiny and hot space at any given moment. Once this bubble exploded, its contents were able to space far apart and begin to cool down.
During the cooling process, the energy of the explosion began to form into matter, eventually forming into protons and neutrons. Once the temperature cooled to 1 billion degrees Celsius, the protons and neutrons were able to come closer together and form nuclei of the elements helium and hydrogen. It may be helpful to show the children a diagram of an atom and point out the protons and neutrons in the nucleus to assist them in grasping these concepts.
Finish the lesson by informing the children that 300,000 years following the big bang, astronomers believe the temperature cooled enough for the nuclei to attract electrons, allowing for the formation of atoms, which are the building blocks of all matter. Reinforce the significance of this by telling the children how literally everything they encounter in their daily lives, from the hair on their heads to the paper they do their homework on, is made up of atoms.