"Wh"-phrases in Mandarin have an interrogative (like English "what") and an indefinite (like English "a/some") interpretation. Previous comprehension studies find that children can access both interpretations around 4.5 years old; studies with younger children focus on production and find that children between 2 and 4.5 do not reliably produce the indefinite interpretation in naturalistic speech or in elicited imitation tasks. In this article, we use comprehension tasks to examine 3-year-olds' interpretation of "wh"-phrases. We find that they have adult-like interpretations of "wh"-phrases in two different contexts: in "dou"-sentences (Experiment 1), where the indefinite interpretation is the only available interpretation and the whole sentence receives a universal reading (roughly equivalent to English "any"), and in negated sentences (Experiment 2), where the interpretation of "wh"-phrases depends on prosodic prominence and the indefinite interpretation leads to an existential reading of the sentence.