I’d buy a large adjustable spanner, hammer, rubber mallet, screwdriver set, calliper (slide rule), small socket set from a decent hardware (halfords) place. Then look to brands like icetoolz for the bike specific bottom bracket tools, chain tool and allen keys. Superstatr mtb for headset tools and maybe splash out on a decent chain whip tool like the pedros one that will avoid the kids punching the cassette (blood) on their first attempts.
Also, spend money (Park tools) on decent cable cutters.
Be an idea to have a home made peg board with the tool outlines on it (if you have space) that way you can instil returning the tools (respect) in the kids and see what’s missing at a glance.
If space allows, pick up a vice from machine mart, plus gas penetrating lube, GT85, Degreeser, clean rags, chain oil, grease, brake and gear cables (inner + outer) + some single / 8spd / 9spd chains that you can use for spares.