Business is one of those things that is a really relevant and useful skill, but is so often neglected in childhood education.
Kids can greatly benefit from learning basic business skills, and operating micro-businesses.
Learning the value of money, and how it is made are valuable life lessons that will help a lot in the future.
A simple thing like a freezie or Lemonade stand might be the first things to come to mind when it comes to kids and businesses, but there are other options. That said, let's look at what skills are necessary for that sort of business.
Inventory, they need to purchase it and prepare it. Understanding that they can take some amount of money, add value and create more money is a important thing that teaches self-worth.
It also requires a understanding of value. In order to produce income they have to make sure their costs are lower then their price.
Inventory also costs money, which they may or may not have. If not then it is a loan that might get them there. Now a loan should have interest attached to it, as in the real world that's how it works. The other thing a loan does is teach long term thinking. If they borrow $10 for supplies, generate $25, pay back $11 (10 + 10% interest) they have 14 left. If they reinvest they will make more next time... if they spend it they are stuck paying interest again next time.
Or get creative, buy in at $10 for a equity stake where you get a piece of the profits, however they can buy that stake back later if they want. Again, delaying spending the money "now" in order to generate more in the future
In addition to basic money skills comes customer service & sales. Again, hugely valuable skills when they are old enough to enter the workplace and to be able to understand how the service industry works. Kids are blasted with ads constantly, what happens when they start thinking about those ads, how they work and trying to create their own sign? I'd encourage them to not just look at their own ads, but to start paying attention to the ads they see and what those ads are attempting to influence.
Does it need to be a food / beverage stand? Of course not, kids have all sorts of options available to them depending on their age. Other standard kids jobs like babysitting, yard care, shovelling, dog walking, window washing, car washing, etc. are all options.
But kids are also creative, maybe they can come up with something new? If they are obsessed with spinners maybe they can make them and sell them? Maybe they can sell old toys or flip garage sale finds on kijiji? Maybe they can create something entirely unique to them and do something with that?
The next thing to look at is persistency, consistency and adapting. A one day stand might do a little money. But if they commit to every Saturday from 11-1 or any other consistent schedule they might start finding repeat customers and referrals. If they shovel a driveway once that's good, but if they commit to every snowfall they can get regular customers. Things build momentum in any business or really any job. And if things really aren't working... why? and what ideas do they have to fix it?
Academic education is only part of the picture when it comes to building the skills that a kid will need to crush it as an adult. If they have a interest in money and business it is never to young to start learning.
btw - if you feel odd taking interest, royalties or renting out your rake and lawnmower to your own child keep in mind the reason, the goal is to teach about money and those sorts of things are important in how money actually works. Feel free to put it away and give it too them later, or buy them something with it.