Run Wild, Run Free (1969)

Philip Ransome, a boy from the west of England about ten-years-old, has been mute since age three and spends his days roaming the moors alone. His parents despair of a cure. One day, he sees a singular wild albino pony with blue eyes and befriends it avidly. A kindly retired Colonel, who accepts Philip as he is, a girl his age, and a pet falcon she gives him provide him with more things to love and care about. Gradually, Philip emerges from his shell. But the way out is full of heartbreak and setbacks.