They wouldn't be mature enough to know the gambling strategies and might lose a lump of money in a go.
As far as I'm concern how about those advanced kids that know the I/O of gambling and the internet even below 18 or the age restriction? I think there might be a rare scenario like that and those companies may never know.
Gambling companies should have strict restriction towards investments and losses, if the investment and losses tend to go beyond a limit, they should be freezing the account for certain period of time.
It's good if they do but I think most of these companies only care about the profit they can make from investors and gamblers, they'll only freeze an account if there's suspicious about it. It might be a good idea but that depends on a certain kind of player like high rollers and not but I have doubts this will never be implemented.