Plural morphology in English is associated with a multiplicity inference, e.g., “Emily fed giraffes” is typically interpreted to mean that Emily fed more than one giraffe. It has long been observed that this inference disappears in downward-entailing linguistic environments, such as in the scope of negation. There are two main approaches to this puzzle: the first proposes that the plural is ambiguous, and invokes a preference for stronger meanings (Farkas & de Swart 2010), while the second derives multiplicity inferences as implicatures (Spector 2007; Zweig 2009; Ivlieva 2013; Mayr 2015). In this paper, we report on two experiments comparing how adults and preschool-aged children interpret plural morphology. The first experiment reveals that both adults and 4–5-year-old English-speaking children compute more multiplicity inferences in upward-entailing environments than in downward-entailing environments, and more- over that children compute fewer multiplicity inferences than adults. The second ex- periment tested a new group of participants on both multiplicity inferences and the upper-bound scalar implicature of the quantifier “some”. Again, both groups computed more multiplicity inferences in upward-entailing than in downward-entailing environ- ments. More importantly, children computed fewer multiplicity inferences and scalar implicatures than adults, and their performance on the two kinds of inferences was significantly correlated. We discuss how the findings of the two experiments support a scalar implicature approach to multiplicity inferences, while posing a challenge for the ambiguity approach.