As a profesional investor I will echo the sentiment to encourage learning fundamentals and discourage app-based investing, meme stocks, etc.
IMO it would be very beneficial for them to learn how a business operates and makes its money. Many people are totally clueless to this but it is pretty foundational in investing.
To do that I would get them to pick a business they want to learn about, task them with writing a report on the industry/business, and come up with a recommendation on whether or not the family should invest $X in the stock (the least important part).
Let's say they pick Nike. Nike is a publicly traded company that files annual reports called 10Ks with the SEC. In the first half of these filings Nike (or any other co) will give an overview of their business - what they do, how they make money, etc. You will also have graphics showing this like sales breakdowns between countries. In addition there are plenty of business breakdown podcasts (
https://podcasts.apple.com/us/podcast/s16e2-nike-business-breakdown-can-the-iconic-brand/id1509069589?i=1000680892095), books, and news articles on Nike to reference.
How does Nike make money? Who buys Nike shoes? How much does a shoe cost to make and what is the breakdown? What do sponsorship deals look like? Why does Nike pursue sponsorship deals? What does Nike market share look like today and what direction is it trending? All examples of quesitons to answer to give a better idea of what this business actually is.