BMI at East Midlands have often had classes round and they get shown round jets in their Maintenance base, not seen any this year but they used to visit by the coachload.
I was also at Cosford Museum about a month ago and there were 3 or 4 coachloads doing the tour then, most of the Aircraft there are simply fenced off as such by a 2 or 3 inch high fence type thing, they were well controlled and seemed to be enjoying themselves, if a little noisey
they must of been in the 7 or 8 year old range and even waited whilst I took photos of the Aircraft off their own backs without being told by teachers, as I did for them when they were doing the same..
One thing you will need to check is your insurance..... and make sure you are covered.