Among the many things one can find to do in London, there is also the National Transport Museum. Kid friendly, spend easily 1 to 3 hrs (or perhaps more) learning the history of transport in and around london. The top level is the oldest stuff, so the story starts there (Why? No idea...)
Further there's some nifty but pricey model trains for sale -- OO-scale, which as I get it are HO-track sized & they help fund the place.
https://www.ltmuseumshop.co.uk/models/full-collection
I'm hoping one day to get something myself, so I can't directly recommend any of it at this time.
(I believe all the bachmann produced items are DCC)