A Hundred Million Francs: Paul Berna

A bunch of scruffy urchin kids in the backstreets of Paris outwit thieves to uncover the whereabouts of millions of francs stolen from the Paris-Ventimiglia express. Gaby is the leader, but it is super-cool Marion with her collection of stray dogs who is the heart of the gang.
It all begins when a local villain offers the children a fortune for their `horse` - a headless rocking horse, given old tricycle wheels that they `ride` down the steep cobbled street, but they don`t want to part with it. Then, a few days later, the horse is stolen, and so begins an adventure that is full of twists and turns, leading to a satisfying conclusion when the villains receive their comeuppance.