Okay kiddo, so imagine you're playing a game of knights and horses with your friends. You have different types of knights, and some of them have big, strong horses that are really good at charging into battle.
That's what heavy cavalry is! It's a group of knights that ride big, strong horses into battle. These horses are trained to charge at the enemy and knock them over. The knights on top of these horses wear heavy armor to protect themselves and their horses from harm.
Heavy cavalry was really important back in the olden days when people fought wars on horseback. They could charge into the enemy's ranks and cause a lot of damage.
But heavy cavalry wasn't invincible. They had a hard time fighting against enemies who were on foot or had weapons that could pierce through their armor.
So, heavy cavalry was a powerful force on the battlefield, but they had their weaknesses too.