Nuria Sajjad and Selena Lau, both eight, died when a Land Rover crashed into the grounds of The Study Preparatory School in 2023.
The memorial event, held on Wimbledon Common, saw benches dedicated to the girls covered in flowers and messages.
Last June the Crown Prosecution Service said it would not charge the 48-year-old driver, as she had suffered an epileptic seizure.
