How could I describe the Save icon to a kid.
Problem: kids don't know anymore what floppy look like.
If you have, by chance, an old cardboard box in the basement with your old floppy disks, now is the time to fetch one and tell the child where all this came from.
Then you go away to your wing chair over at the fireplace and pull out your pipe and your glasses.
Seriously, the best explanation is by showing it. Try get an old floppy disk and tell the kid, what it was useful once.
Maaaahh bleet bleet. ("Kid")
With kids these days it's all about the ram.
...I should stop now.
In all seriousness though, the metaphor is broken.
Until then, Ctrl+S, and don't worry about the explanation unless the child expresses a specific curiosity.
While I understand your question it's not really an issue.
As long as the icons on a toolbar are easily distinguishable from each other what they look like isn't a big issue. Yes it does help, but not as much as you'd think.
Back in the late 1980s/early 1990s I was working for a company that sold it's software all over the world. This was before PCs took off so we were selling on high end workstations, but localisation and internationalisation was a really big issue - it took a lot off effort to translate applications.
The MD had the idea to use icons everywhere so that there'd be no text to translate - even in the user manual. We didn't get there, but on the way we discovered this fact about icons.
We initially tried to make the icons representative of the option/command. While this was easy for some cases, others were very tricky. It was then that we discovered that people didn't remember what the icon did because it represented the action, but because it was sufficiently different from all the other icons. So it didn't matter if save was a picture of a floppy disk or just a squiggle.
So just drill into your kid that the save icon is that funny little blue square (or whatever) and they should remember which one to use.
Tell them to hit
That's the keyboard shortcut in 99% of applications.
Life preserver, File cabinet, A Zipper
Just think of things which "save" or "protect".