Science Museum is a real time commitment — fit it in only if it's a priority.
Allow 2–3 hrs.
The most kid-friendly of the South Kensington trio — interactive galleries, space hardware, a flight gallery. Free and a guaranteed hit with children. Catch: the best bits (IMAX, simulators, Wonderlab) are paid add-ons, and it's mobbed on rainy weekends and school holidays.