We stayed at Marc's place with our 7.5 year-old son. The place looks very nice and is well equipped. Make sure you have an adaptor for the outlets, you may also buy one at a store close by. We left one in the apartment :)
Windows seem a little unsecure but I guess this is a problem with older buildings. The location is a little bit far from the city center, we mainly used the bus to get there, so it took some time with the traffic in London.