Hey, which district of London do you plan to stay in? There are 32 boroughs in London. All are good places. Your choice of locality should depend on your budget and the size of your family. I have been to some great neighbourhoods in London, liked them all so far. Notting Hill, Chelsea, Aldgate, Shoreditch, Mayfair, Kensington are all great places to stay with a family.
Will you be working somewhere in London? If yes, what would be your average salary? Keep around £2000 spare for accommodation. An average pub meal will cost about £12 while a restaurant meal costs around £25. Add to that the cost of groceries and laundry for two people including toiletries and you get £10. Moving on to average school fees in London-fees for a day prep school is £15,000 per annum while senior school fees is around £25,000 pa.
London is a great place to live. It has superb connectivity and transportation. It has a thriving network of tube and train stations with major connecting stations falling along all the prominent locations in London. Refer to the area guides of London before moving here. Read up a bit about the city and know its culture and history.
Also, if you don't mind can I ask where are you from? If English is a second language for you, make sure you appear for IELTS or any other internationally standardised English proficiency test. Do check with the official government website of UK at Gov.UK for the regulations.