Dear little one,
A small engine is a machine that helps make things work using gas or electricity. It is called a small engine because it is smaller than the engine in a car.
A small engine has many parts that work together to make it go. One of these parts is the spark plug, which creates a spark that ignites the gas and makes the engine run. The fuel tank holds the gas that the engine needs to run.
The engine also has a carburetor, which mixes the air and fuel together so that the engine can burn it properly. The air filter helps keep dirt and other nasty things from getting into the engine and clogging it up.
Finally, the exhaust system helps the engine get rid of the gases that it doesn't need anymore. This is important because those gases can be harmful if they stay inside the engine too long.
People use small engines for all sorts of things, like lawn mowers, chainsaws, and even snow blowers. They are really helpful because they can do work quickly and easily - but mostly they are so small that we can carry them easily!
I hope that helps you understand what a small engine is all about. If you have more questions, just ask!