Okay kiddo, so a cadre in the military is a group of really important people. They are like the boss and they make sure that everyone else knows what they are doing and how to do it.
Imagine you are playing a game of soldiers with your friends. The cadre would be the one who makes the rules, tells everyone what to do, and makes sure that everyone is following the rules.
In the real military, the cadre are usually experienced soldiers who have been chosen to be leaders. They are responsible for making sure that the new soldiers are trained properly and that everyone is ready to do their job. It's kind of like having a teacher who helps you learn everything you need to know.
So, the cadre is a really important group of people who keep everything running smoothly and make sure that everyone is doing their part.