Epic,
Too bad you and your company decided on going to London; I would have suggested Oslo instead.
I've been to London several times in the summer, assuming it isn't also raining on top of everything it's generally noisy, often dirty and smelly, and pretty much ALWAYS crowded. You'll almost have to elbow your way along even when alone, I can't imagine what it must be like in a party of four with two baby strollers on top. It will be stressful.
Driving in London is more like shuffling along narrow streets at slower than pedestrian speed while the car in front of you farts (diesel) exhaust in your face.
Oslo, while being a major city, also has a bit of congestion of course, but not nearly on the same level. The city itself is simply beautiful, growing up the surrounding hills along the fiord, with lots of nice shopping streets and notable tourist attractions, including the Karl Johan Street with the Royal Palace, the Vigeland Park, the Colosseum cinema and the Kon-Tiki museum to mention but a very few.
Norwegian nature is striking, it's a quite mountainous country and offers many breathtaking views once you gain some elevation, and going for a spin in a car can be an experience in of itself as you drive along the curving road of a steep valley.
Oslo's not a cheap city, but then again you're planning on going to London so that must not be an issue for you anyway...