Okay kiddo, a borate ester is like a special type of molecule that is made up of boron, oxygen, and some other atoms. It's called an "ester" because it's formed from the reaction between an alcohol (which we can think of like apple juice) and a special compound called "boric acid" (which is like vinegar). When these things combine, they make a borate ester molecule.
Borate esters are very useful because they can do some cool things. For example, they are often used as fire retardants in things like furniture and clothes. That's because the borate ester can actually help stop fires from spreading by releasing water when it gets hot. The water then helps put out the flames before they can get even bigger.
Borate esters are also used in some cleaning products to help get rid of bacteria and fungus. That's because the boron in the molecule can help kill these harmful things.
So, to sum it up, a borate ester is a special type of molecule made from boron, oxygen, and other atoms that is useful for stopping fires and killing bacteria and fungus.