The best museums for toddlers in London are the Young V&A in Bethnal Green (fully hands-on galleries), the Science Museum Garden gallery (water play and building for ages 3-6), the Natural History Museum (dinosaurs and blue whale), and the Horniman Museum in Forest Hill (music gallery where kids can play instruments).
Most major London museums are free for everyone, including the Natural History Museum, Science Museum, Young V&A, British Museum, Tate Modern, Tate Britain, National Gallery, National Portrait Gallery, Horniman Museum, RAF Museum, Imperial War Museum, and London Museum Docklands.
The most interactive museums for kids include the Science Museum (Garden gallery with water play), Young V&A (three fully hands-on galleries), London Museum Docklands (Mudlarks free soft play gallery), Discover Children's Story Centre (immersive story trails), and the Postal Museum (underground Mail Rail ride).
Most free museums in London do not require booking, though some popular galleries like the Science Museum Garden need a timed slot. Paid museums like the London Transport Museum and Postal Museum should be booked online in advance for the best prices. Weekend mornings are busiest at all venues.