- Well, you can't sing that.
- Oh, do let her. She's such a sweet little thing.

4 seconds sound clip from the Meet Me in St. Louis (1944) movie soundboard.

You can hear this line at 00:33:09.610 in the DVD version of the movie.

Quote context

[...]

- I want to sing too. One song, all right, Rose?

- Well, if they promise to go right up.

- All right, Agnes, that's enough fudge.

- Tootie really sings quite well for a child.

- What would you like to sing, dear? Baby's Boats, A Silver Moon or Did You Ever See a Rabbit Climb a Tree?

- No. I hate those songs. I want to sing a new one. It goes: I was hmm last night, dear Mother

- Well, you can't sing that.

- Oh, do let her. She's such a sweet little thing.

- Sweet? She's a hoodlum.

- Oh, come on, let her sing.

- Well, all right. Go on. Go on, Tootie.

- I was drunk last night, dear Mother I was drunk the night before, but if you'll forgive me, Mother, I'll never get drunk anymore.

- Tootie, you're a very bad girl. It's really Lon's fault. He teaches her those things.

[...]