We took the DCs to Gullivers in Milton Keynes for Hallowe'en 2 years ago. (They would have been 10 and 7.6 at the time)
I read the online reviews and thought I had seriously blundered and considered not going (it's a 1.5 hour journey for us) but we'd paid £45 for the tickets.
Really glad we went.DCs loved it. The rides are all child friendly. The staff were really good (some didn't say much to the children but none was rude, which the reviews said they were). Quite a few were really chatty with the DCs.
Toilets were clean, food was okay.We took a picnic for lunch and had pizza/baked potatos later.
There was a really good fireworks display at the end.
Christmas would be really special there IMO, if Hallowe'en was anything to go by. Only thing stopping me is my DCs are too old now.But Gullivers is ideal for maybe up to 10 yo.