Parents must not only understand about bitcoin, or saving, or investing in general, but they must educate their kids about finances as well. What is the point of running a child savings account, if the kid withdraws and spends all of them when he turns 18. Also parents must be very confident in banks. For example my grandmother during Soviet times was saving money on "
passbook" for many years, and with time redenomination has happened and 1000 turned into 1. Banks can go bankrupt. People must be very cautions with savings.
I would say that if you hold it until 18, rest is not really that crazy because while 18 is not enough to make super smart choices I would say that it is not going to be too young neither. Depending on the reason why they want to divest, it could be fine. Remember, we do invest for our future, but if you always keep on investing for the future, you will never have time to divest, I do not want to die without repaying the benefits of my investment.
If a kid says he is going to buy a lmabo at 18 with all that money, yeah do not let him, but if he says he got accepted at Harvard and needs to cash the investment in order to pay for their education? Well I can't think of any better reason, that would be lovely. So, it all depends on what the kid wants to use it for.