Hi are there any evening entertainment family friendly mid week , last week in August ??
You could try looking for listings on the Bath Chronicle website.
The Roman Baths stay open late in August (last Admission 9pm). A lot of shops will be open late on Thursday 23 August if you are there that week. otherwise get some ideas from the visitbath website.
I've not found time to take my daughter on the Bizarre Bath comedy walk, but I do recommend it.
If you fancy something more active, hire some bikes and cycle along the canal towpath or on the Two Tunnels cycle path to a pub (or walk for that matter).
If all else fails, the sports centre has ten pin bowling, and a small trampoline park.