This paper examines what children believe about unmapped number words--those number words whose exact meanings children have not yet learned. In Study one, 31 children (ages 2-10 to 4-2) judged that the application of "five" and "six" changes when numerosity changes, although they did not know that equal sets must have the same number word. In Study two, 15 children (ages 2-5 to 3-6) judged that "six" plus more is no longer "six," but that "a lot" plus more is still "a lot." Findings support the hypothesis that children treat number words as referring to specific, unique numerosities even before they know exactly which numerosity each word refers to.