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If a child can operate an android device properly, play video game, use communication gadget, use different computerize device etc. why will I not introduce them gradually to Bitcoin. Digital currency is the future and should I not be responsible enough to start channeling them gradually to that direction. I don't agree completely that kid cognitive processes lack awareness, consciousness, and the ability to maintain a sequence of thoughts in their minds.
Note: It is in record that Tiger Woods turn Professional Golfer at 20 but was expose to golf at child hood.
But don't forget those require less responsibility. For example, if you forget password of social media, you could just ask to reset password. But Bitcoin require higher degree of responsibility and there's no "undo button" when you make mistake.
Is buying Bitcoin or cryptocurrency good for Kids?
Yes,
assuming they're being responsible with fiat money and aware of risks of owning cryptocurrency (primarily unstable price).
Should authorities or agencies place age restriction on owning Bitcoin?
No, especially because kid is legally allowed to own money and even have opening bank account (usually with some supervision or feature limitation)