I went to London with my 7 y/o son for a couple of days and this was just the best place to stay for us.
A bit outside the city center, so it isn't as busy or as smoggy, West Hampstead looks more like a town. There are shops and some nice little restaurants and bakeries, so we had some of our meals there.
Within 20 mins (including the walk to the station) you're in Central London by underground, overground or Thameslink train. There's also a bus stop nearby, but the bus takes a bit longer. So you've got many options to get where you need to go.
The accomodation was perfect for two. It's very neat and clean. The rooms are light and spacious. The bed was very comfy, the bathroom is great with a walk in rainshower and a bath and it was just lovely to have a lounge where I could relax while my son was sleeping in the bedroom.
Sue and Robert are very nice people and great hosts. We were well taken care of and it was so nice to talk for a bit about our day when we got "home" in the evenings.
I can very much recommend this Airbnb and would definitely stay here again the next time we go to London.