Institute of Astronomy in Cambridge hold public evenings that are free during term time (October to December and January to March). You can see the telescope that is over 150 years old and if the sky is clear, you can have a look.
There are talks given by PhD students and you can see the talks that they will be giving. You can also arrange to bring a group to these events and they can tailor it to all the age of the audience. I brought my brownies here and they loved it!
All the Best!
American to Britain