I live in Greater London, but I remember what it's like to feel like a tourist in this big city. There are a large number of sights, attractions, bars and restaurants in London, and I'm sure there's enough variety to give any traveller a good experience.
If you're going to stick to Central London, don't hire a car. Get yourself an Oyster Card, charge it with money or a Travelcard, and use the public transport network. The London Underground is the quickest way to get from one place to another, but the buses are my preferred form of travel. You get a much better idea of how London fits together if you travel by bus. Between 07:00 to 09:00 and between 16:30 to 19:00 you're better off on foot, because city workers flood the transport systems during these hours.
For an interesting walk that takes in some of the most famous sights, start at Victoria Station and head east along Victoria Street. You'll pass Westminster Cathedral and then Westminster Abbey before reaching Parliament Square, where you'll see the Houses of Parliament. Then head north along Parliament Street, which becomes Whitehall, and you'll pass The Cenotaph, then Downing Street and Horse Guards on your left before reaching Nelson's Column in Trafalgar Square. From here you're pretty close to Leicester Square and Covent Garden, both of which offer bars and cafés to relax in. If you're not up to the walk, there are buses that follow this route.
Camden is worth the journey into north London if you're looking for alternative culture. Very close to Camden Town Underground station is the Electric Ballroom, a long-established venue that hosts live music gigs and club nights. During the day, the Electric Ballroom is just one of several places that hold a market in Camden, and these markets sell alternative clothing, accessories, crafts, antiques and other goods, seven days a week.
London has many great museums. The Science Museum and Natural History Museum are next door to each other, not far from South Kensington Underground station, and both should keep children entertained. The Imperial War Museum is located in Lambeth, not too far from Waterloo. The British Museum, close to Tottenham Court Road, is one of many museums found along Museum Mile. Entrance to most of the popular museums is free.
The list of attractions in London is huge. London's West End is famous for its theatres, and nearby Bond Street, Regent Street, Oxford Street and Tottenham Court Road should be enough to satisfy shoppers of all classes. London Zoo is home to a large variety of animals, though be warned that the squirrel monkeys have acquired a taste for mobile phones. The Tower of London is a fascinating place, and it's situated right next to Tower Bridge on the River Thames.