The legality of teaching children how to trade cryptocurrencies depends on the country and the specific laws and regulations in force. Many countries do not have specific laws governing cryptocurrency trading. It is important for parents to learn the laws and regulations in their country or region and exercise caution when allowing their children to trade cryptocurrencies.
I do not think that is totally true, you can see many centralized exchanges that do not require anything more than email and password to trade, although some can demand for KYC, but what about those decentralized exchanges that you can also be used to trade. I have seen it on pancakeswqp that you can even do future trading which only what you need to do is to send coins to your noncustodial wallet and connect the noncustodial wallet to the decentralized exchange, using the coin on your noncustodial wallet to trade without any identity needed and the control is totally yours.
It's okay, let them explore things like trading as it will enrich their critical thinking and will urge them to know more about the financial market. Every learning should be supported when your kids are very excited and craving to do it. Showing them that you support them will make them optimistic that there should be a good result of what they are trying to do. It's risky because there's money involved but trading isn't limiting everyone to just have a set of budget like a couple of bucks or minimum amount that's required by an exchange.
To me it is not a good advice for children to trade, but you can start teaching them the basics and what that is required and how risky it is with real life past events of people that have lost huge amount of money to trading. What I just meant in my first post is not about age of 10, 11, 12 which are very small, even 14 is still very small, but just that a friend is asking a friend about how to trade, if he continues to discourage him and he persistently want to know how to trade, there is nothing bad to teach him, but letting him to know the wrong side of trading and how it can turn a rich man to a poor person. As a friend, I can teach, and as a father, uncle or brother, I can teach but not in a way to let the child trade, but as a step to what he many know in the future.