The London Children's Book Swap
Time Out says
Share your pre-loved books and make space for some new favourites at these book swap events, taking place across multiple London boroughs. Children are encouraged to bring in stories they're ready to pass on and exchange them for undiscovered ones, with many of the events featuring free entertainment and activities, too. The Discover Children's Story Centre are behind the initiative and participating venues include V&A Museum of Childhood, The Cartoon Museum, Southbank Centre, Hackney Picture House and many London libraries. See the event page for more details.