The, uh, explanation for this is all very simple.
5 seconds sound clip from the Miracle on 34th Street (1947) movie soundboard.
You can hear this line at 00:21:02 in the Blu-ray version of the movie.
Quote context
[...]
- Oh, come now. You must want something.
- Whatever I want, my mother will get for me - if it's sensible and doesn't cost too much, of course.
- Hello, Susan. Hello, Mr. Gailey.
- I think you've taken up enough of this gentleman's time. Come along, dear.
- The, uh, explanation for this is all very simple.
- Cleo's mother sprained her ankle. She had to go home. So, she asked me to bring Susie down to you.
- Yes, I know. Cleo called me. I've been wondering where you were.
- I thought, as long as we're here, we might as well say hello to Santa Claus.
- He's a nice old man, Mother, and those whiskers are real too.
[...]