I think if you take a look at Visit London website you might be reassured. I don’t know what people are imagining but it’s not very controversial unless you truly believe that any sexuality other than heterosexual is inherently wrong.
There are some good openers for discussion on display like the door of Oscar Wilde’s cell in Reading Gaol or Alan Turing’s contribution to victory in WW2 and his subsequent shaming.
The overall ethos is of acceptance of who a person is and acknowledgement of all that “Queer” people have contributed to society, whilst having to hide their sexuality. Perhaps there are a few surprises sitting there for many people.
In regard to the age group, 11/12 years old is when most children are experiencing puberty and becoming aware of sexual feelings. It’s also when bullying about sexuality starts to come to the fore.
I think the visit is well-timed and hopefully will lead to discussion, not just about sexuality, but about being perceived as being ”different” in all sorts of ways.