I tell her Santa Claus is a myth, and you bring her down here, she sees hundreds of gullible children, meets a very convincing old man with real whiskers.
9 seconds sound clip from the Miracle on 34th Street (1947) movie soundboard.
You can hear this line at 00:21:38 in the Blu-ray version of the movie.
Quote context
[...]
- Susan, would you stand over here a minute? I want to talk to Mr. Gailey.
- I shouldn't have brought Susie to see Santa Claus, huh?
- Now, you're making me feel like the proverbial stepmother.
- I'm sorry, but it's just that I couldn't see any harm in just saying hello to the old fella.
- We were talking about Susie, not about you.
- Well, whether you agree or not, I must ask you to respect my wishes regarding Susan.
- She's my responsibility, and I must bring her up as I see fit.
- Okay.
[...]