I don't know if you've ever looked into a merlin pass?
We have them and it's so worth it.
They don't need one anyway under 3 years but even as adults, you pay £30 each to get the passes and then £9 each a month.
And then you get Alton Towers, chessington, all the sea life's, loads in London like the London Eye, madame tussards, shreks adventure, London dungeons. Anything that is Merlin owned basically.
It was the best thing we did, just being able to decide, ahh let's go here. And only have to worry about food and fuel.
Considering you pay £20pp for sea life ect
Also to add on that lots of cereal boxes I've seen have the 2 for 1 on Alton Towers ect at the minute too