There are two different anecdotes about that character that I love.
The first is Dick Van Dykes story of the day they were shooting the scene with the Child-Catcher on his horse drawn cart, and it went out of control. Sir Robert Helpmann, who played the Child-Catcher, had been a noted ballet dancer for forty years rather than actor and when the the horses galloped, he stayed on the cart, trying to steer it. When it rounded a corner and tumbled down a hill, he managed to jump on to the wagon itself, stepped across it as it tumbled underneath him, and landed gently on the ground without a scratch on him. As Mr Van Dyke put it "It was the most graceful damned traffic accident you ever saw"
The other is that Sir Robert Helpmann, though never an easy man to work with, was by all accounts wonderful with children, completely at odds with the Child-Catcher role. He was godfather to numerous children, and in one instance they were absolutely petrified when they saw their "Uncle Bobby" as the Child-Catcher, to the point of nightmares. Their parents phoned Robert up and asked him to reassure the kids that he was still their "Uncle Bobby". He agreed and when they were put on the line to speak to him he couldn't resist and actually said the "Lollipops! Ice-Cream! Chocolate!" to them. Cue more screaming in terror... You gotta a love a man like that! (I'm a firm believe that a little mindless terror is a healthy thing in a child's life)