40 Spanish-speaking children aged 3-5 were tested on their interpretation of un 'a/one' and other numerals and quantifiers in a truth-value judgment task and a sentence-picture matching task. Children performed significantly better with dos 'two' and tres 'three' than with un. Unlike English-speaking children, Spanish-speaking children assign un an 'at-least' reading, as they do for the quantifier algunos 'some' (see Barner & Bachrach, 2010), even after learning the 'exact' meaning of higher numerals, consistent with claims that un is only an indefinite and not a numeral (a.o. Kayne, 2009). Additionally, it was found that Spanish-speaking children are relatively delayed in the acquisition of the exact meaning of two and higher numerals as compared to English-speaking children. These results provide further evidence for the hypothesis that the acquisition of numerical concepts can be accelerated or delayed by the morphosyntactic use of number and number words, and that the (lack of) exact meaning for numerical concepts is at least partially bootstrapped from the language system.