Unusually for the time, Walt Disney insisted on children providing the voices for the animals in Bambi when they were young, instead of using adults mimicking youngsters.
Six-year-old Peter Behn auditioned with several other children for the voice roles of Mother Rabbit’s children. When Behn said the line (in reference to Bambi), “Did the young prince fall down?”, a casting director who was watching the audition in another room shouted, “Get that kid out of here! He can’t act!” However, the Disney animators who heard the audition tape loved the sound of Behn’s voice. Behn was called back to the studio, and the character of Thumper was created largely based on his vocal performance.
Donnie Dunagan, who was the voice for young Bambi, also was the model for Bambi’s facial expressions.