Personally I would say that kids and teachers alike should get into the habit of wearing them when doing almost any experiment as it's such a simple measure that can save such a delicate and useful sense.
My eyes have been saved 3 times in my 6 years of being a chemist from a injury that would have likely blinded me and there have been countless times I've have splashes from washing up with acetone/methanol/dilute HCl that would have hurt like a bitch and I'm thankful to my teachers for being draconian about wearing safety glasses now.
Obviously with COVID some schools are going to struggle with needing to sanitise goggles etc. and unless the experiment calls for an acid/base, stain, risk of something breaking into shards, spring flicking into eye etc. then one could consider no glasses, but only if the risk is incredibly low. For the alkali metals demo, bits of metal can fly over a screen so kids should DEFINITELY wear eye protection as although the chances of a grain of flaming metal goes in a kids eye is very low, IF it happens to land in an eye, the damage to the eye would be catastrophic. It's just not worth the tiny risk when all it takes to mitigate is wearing glasses.
I do think that ideally kids should be given a pair of safety glasses with a case to stop scratches at the start of the school year, like any adult would be given a set of PPE when starting a job but there will be numerous issues in various schools (cost, storage, forgetfulness) and many creases to iron if such a system was put into place. My sixth form had this in place which worked for us, but we were sixth form and were more organised than the average 11 year old.
