Join a Street Art Walking Tour
London is home to some of the best street art in the world. The walls around east London are covered in work by ever-changing artists. Shoreditch in particular, near the Liverpool Street station, is always a great spot to start a street art walk. You're likely to see everything from intricate works by world-renowned artists like Banksy all the way to colorful tags by locals.
Teenagers often enjoy photography and this would be an excellent opportunity to get some cool shots of 'real London' for them to post on social media.