Mm.
Depending on how young these children are, how inquisitive they are, and what you think they might find interesting, there's this one you could look at:-
"Sugar On a Stick"
Developed by Sugar Labs, it's an OS specially designed for youngsters, with interactive 'learning' built-in. It'll run completely from a USB stick....2 GB or larger. (I doubt you'll find anything under 16 GB these days, but even those are as cheap as chips).
Before deciding, you can try a 'Live' version of it on-line, to give you some idea:-
https://try.sugarizer.org/
If you think it may 'fit the bill', download/installation instructions are here, at the Sugar Wiki:-
https://wiki.sugarlabs.org/go/Sugar_on_a_Stick/Installation
Of course, if we're talking about teenagers then they're already interacting with the online world, and full of curiosity anyway. It's a rare teenager that can't figure out tech pretty quickly.
That being the case, any of the lightweight distros would do the job. I won't recommend my own 'daily driver', Puppy Linux, because it's rather more 'manual' & 'hands-on' than many, and most people, even youngsters, like things that are straight-forward and easy to use.
Mike.
