What should a kid, that is under working age, invest in?

I don’t mean like investing in a stock or in a crypto currency, which could be done, I mean like investing their time in doing to make money. For example making something and then selling it to freinds at school. I prefer to make origami then sell it. It is a pretty profitable buisness. I have also made transforming ninja stars and that was a very successful buisness. You could also make things out of wood but that not be as successful. There are some things that could be made in minutes and some in hours. You could also do favors for money like asking someone out for someone else. These would all be possible ways to make some money but there are still a lot more ways to make money. I might expand more on this topic but probably not.