Kid's Guide to Matter

There are three basic states of matter: solid, liquid, and gas. Everything on Earth is made up of microscopic particles (molecules, ions, or atoms), and the speed and density of these particles determine which state of matter and object is. The properties of the three elements are very easily defined and identified.
Solid
A solid is anything that holds a particular size and shape. An apple, a block of wood, and a penny are all solids. The only way they can change their shape is by force (for instance, if you bite the apple with your teeth or chop the block of wood with an ax).
The particles in a solid are tightly packed and don't make a lot of movements.There is not much free space in between the particles, so there is very little room for the particles to move.
Liquid
A liquid is anything that has size or volume, but does not have a shape. Liquids must be contained in a cup, bottle, or receptacle in order to have a shape. Milk, water, and juice are liquids. When you pour milk into a glass, it takes the shape of the glass. If you spill the glass of milk on the floor, it will spread quickly as it takes the shape of the floor.
Liquid particles are not as close together as particles in a solid, and move around and past each other much more freely. They have no regular shape or arrangement and move freely.
Gas
Gases are hard to identify because they have no color or shape. Take a deep breath and feel your lungs get bigger. Your lungs are filling up with air, and air is a combination of many gases. It has no shape or size.
The particles in a gas move freely at high speeds. There is a lot of free space in between the particles, and they take the shape of any container
Resources for Kids
The following links may help you understand the different states of matter:

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