The present study reports a large, cross-sectional study of Mandarin-speaking children's ability to compute quantity implicatures. To chart the developmental trajectory of this pragmatic ability, we tested 225 Mandarin-speaking children aged 4-8 years on their interpretations of scalar and non-scalar implicatures, as well as numerals. Scalar implicatures were difficult and we did not observe consistent success until age 6. In contrast, by 4 years of age this group was already able to compute non-scalar implicatures and the exact readings of numerals at adult-like rates. The implications of the current findings are discussed in relation to children's development of pragmatic inference, highlighting the relevance of cross-linguistic data in understanding pragmatic development.