The computer immediately shows spelling errors and corrections, TEACHING correct spelling.
> The videos are more about funny jokes than the different phases of matter.
( youtube is a funny one. Non-there are many great youtube channels packed with scientific content, like Smarter Every Day, Veritasium, Mark Rober, CGP Grey, VSauce, engineerguy, Physics Girl, Captain Disillusion, Mathologer, Numberphile, ...
> I don't want to have to sit next to them all night making sure that they are only doing 'productive' work.
That's a parenting issue not a computer issue. Teach your kids what's allowed and what's not, and check their browser history until they learn how to manipulate it, then check your router logs
The main problem with ed tech is the extremely low quality of the apps the schools buy and make the kids use, not the computers and youtube themselves.