Yes LT museum shop is good and there's a toy theatre shop in Covent garden as well (Pollocks) and a rather good nauticalia shop if your DC are that way inclined, and a small Disney shop and bloody build-a-bear and other toy shops as well. Or the south ken museum shops are all good.
It's called Mystical Fairies on Flask Walk in Hampstead so lots of nice places around for breakfast/lunch. We usually combine it with a trip to local library next to Keats' house which is in lovely grounds, Daunt Books near Hampstead Heath overground station and the Heath itself.
Flask Walk is just round the corner from the tube station. They also do fairy school/princess academy/drama workshops type things during the school holidays. My DD loves it but she is younger.