Bob the Builder, Pingu and the Fat Controller will be among those taking part in the Children's Society's sixth annual London Bridges Walk on 13 September.
More than 2,000 people are expected to take part along the five- or 10-mile routes. Children can meet and be photographed with television favourites, including a wooden model of Thomas the Tank Engine.
The charity hopes to surpass the £120,000 raised last year.
Bronwyn Friedlander, a press officer at the Children's Society said: "It's a nice leisurely pace and people can stop and have picnics. It's a fun day out."