"The child drank all the milk."

Translation: 아이가 우유를 다 마셨어요.

[Shlomo_]

I meant, when is 모두 vs. 다 correct?

[wintertriangles]

In this case, for the object receiving the action, 다 sounds much better. 모두 is for people, 모든 것 is for things, but still aren't used to receive actions, rather they're used as subjects. Maybe a mod can correct me if that's incorrect.