Objectivism is a really big idea that a smart woman named Ayn Rand came up with. It says that each person is their own boss and they have the right to make their own decisions. That means that nobody else can tell you what to do with your life or your things. It's like when you play with your toys and you make up the rules yourself. Nobody else can tell you how to play because they are your toys and you get to decide how you play with them.
Objectivism also says that people should work hard and be really smart so they can make a lot of money and have nice things. That's because they are the ones who earned it and nobody else can take it away from them. It's like when you do your chores and your parents give you some money. That money is yours to keep and use as you please.
Objectivism also says that people should be really honest and never hurt others on purpose. This is because every person is important and deserves to be treated with respect. It's like when you play with your friends and you share your toys and take turns. This makes everyone happy and nobody gets hurt.
In summary, objectivism is an idea that says you are in charge of your own life, you should work hard to make a lot of money, and you should always be honest and treat other people well.