Most children think a business is a building. It is worth replacing that picture early, because the real definition is both simpler and more useful: a business solves a problem for somebody who would rather not solve it themselves.
Once a child holds that sentence, they start spotting businesses everywhere, including ones with no building at all. The noticing is the actual lesson. The vocabulary can arrive whenever it likes.
A business solves a problem for somebody, and they pay for the help.
A business solves a problem for somebody who pays for the help. A lemonade stand becomes a business when thirsty people want a drink and the stand gives them one.
An entrepreneur is someone who notices a problem and decides to be the one who fixes it.
An entrepreneur is the person who notices a problem and decides to be the one who fixes it. The noticing is common. The deciding is the rare part.