Looking for an accomodation in summer holiday

Hi,
I'm looking for an accomodation with cooking facilities for 2 adults and 4 children (from 6 to 12 years old) from 29th July to 3rd August 2009. The best location would be central London.
If you can help me I'd be grateful because it isn't so easy to travel with four children.
Thanks in advance and I hope to hear from someone soon.
Laurence