I've travelled to London a few times, get the London Pass. It includes admission to everywhere you'll possibly want to go. You should also take the family to a show and you can get tickets the same day at a discount broker. We saw Matilda there last March.
BTW, my twins were 6yrs old when we took them last year and they loved it.
I'd skip the Legoland Amusement Park. Not worth it and you can go to the ione n Orlando.
https://www.londonpass.com/?utm_medi...97178d39c89abe