Have a torch handy...
Oh alright, joke, joke...
Safety glasses, if they come in kid-size, are a splendid idea. Additionally, I'd be looking to keep paper in paper safes, safelight switches high up, chemicals in a locked cabinet, electrical cables on (and preferably fastened to) the benchtop, tools, trays etc where only you can access them (in terms of height/reach) and no more than yourself and one other in there at any time when working (so you can divide your attention — however tryingly — between the stop bath and yelling "stop that!" :-0). Ten to 11 year olds are a handful (my nieces are that age!), while 18 year olds are often mistaken by me to be much older!!

A yearly fee? My goodness, very entrepreneurial! :-)