The easiest way to describe a battalion to a child, in order to aid their understanding of military history, is to stick to the numbers. Thus, a typical battalion consists of 300 to 1200 soldiers.

The Battalion Commander is in charge of a battalion.

battalion alludes to the number of men therein. battalion commander alludes to the commander of the battalion

Well you can search for certain sites that will provide cpr and first aid training in your area. Most classes are held at a police station or fire station.

The word battalion is a collective noun for a battalion of soldiers or a battalion of photographers.