We did Legoland last year. It was amazing. Not much of the park is open, none of the big rides, but it was beautifully decorated. At the appointed time you go to a special bridge by the castle, and are then escorted into a forest of Chrustmas trees. We saw some elves in the forest, but no other families. The wooden FC coins are arranged around the outside of the "forest" but you can't see them until you are in the steps and specifically look, I'm 5'7"
It is expensipve, but you get a hot drink each, the kids get a Lego present (value of ours were each about £10) there were 2 restaurants open, a burger one, and the rotisserie in the castle which served a really reasonable 2 course meal, about 3 choices each for kids and grown ups. I wanted a dessert from the kids menu, and they just laughed and said it was fine (an ENORMOUS sticky toffee pudding)
Apart from the rides, there was also a place to write a letter to Santa, colour Christmas cards and ice a gingerbread man. All included in the price.
We have also done Osterley house (3 years ago) and Ham House (2 years ago) , preferred Osterley, may try Syon this year.