The quantifier "dou" (roughly corresponding to English "all") in Mandarin Chinese has been the topic of much discussion in the theoretical literature. This study investigated children's knowledge of this quantifier using a new methodological technique, which we dubbed the Question-Statement Task. Three questions were addressed: (i) whether young Mandarin-speaking children know that "dou" is a universal quantifier that quantifies over the elements to its left, (ii) whether they know that "dou" is an adverb of quantification (Q-adverb) which can (unselectively) bind any variable in its domain, and (iii) whether they know that "dou" can quantify over "wh"-words. The main finding was that, by age four, Mandarin-speaking children have the relevant knowledge. The results reflect the early availability of adult-like linguistic knowledge of "dou"-quantification.