The Optimists of Nine Elms

The Optimists of Nine Elms, also known as The Optimists, is a 1973 British drama film starring Peter Sellers and directed by Anthony Simmons, who also wrote the 1964 novel upon which the film is based. The film is about an old street musician played by Sellers who strikes up a friendship with two children Liz, played by Donna Mullane, and her young brother Mark, played by John Chaffey. Neither of the child actors were featured in future films. A young Keith Chegwin also played a small role in the film.

Source: Wikipedia