We can't let her down.

3 seconds sound clip from the Miracle on 34th Street (1947) movie soundboard.

You can hear this line at 01:35:25 in the Blu-ray version of the movie.

Quote context

[...]

- Oh, you were right, Mommy. Mommy told me if things don't turn out just the way you want them to the first time, you've still got to believe, and I kept believing, and you were right, Mommy!

- Mr. Kringle is Santa Claus!

- Where are you going?

- To see if there's a swing! There is one! There is one!

- You told her that?

- The sign outside said it's for sale.

- We can't let her down.

- I never really doubted you. It was just my silly common sense.

- It even makes sense to believe in me now. I must be a pretty good lawyer. I take a little old man and legally prove to the world that he's Santa Claus. Now, you know that...

- Oh, no. It can't be. It must have been left here by the people that moved out.

- Maybe.

- And maybe I didn't do such a wonderful thing after all.

[...]