The document provides information on things to do for children in London on Playday, including three family-friendly activities: 1) Sliding Gate at the Southbank Centre features large slides for both children and adults to slide down and an "urban beach" with a water fountain and sand. 2) Battersea Park offers rowboats and pedalos that can hold up to five people to rent on the park's lake. 3) Kensington Memorial Park has a free water play area with jets, pumps, and buckets for children to play in and cool off, providing an activity for hot summer days.