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! :-)