Acoustic-phonetic exaggeration of infant-directed speech (IDS) is well documented, but few studies address whether these features are modified with a child's age. Mandarin-speaking mothers were recorded while addressing an adult and their child at two ages (0 ; 7–1 ; 0 and 5 ; 0) to examine the acoustic-phonetic differences between IDS and child-directed speech (CDS). CDS exhibits an exaggeration pattern resembling that of IDS – expanded vowel space, longer vowels, higher pitch and greater lexical tone differences – when compared to ADS. Longitudinal analysis demonstrated that the extent of acoustic exaggeration is significantly smaller in CDS than in IDS. Age-related changes in maternal speech provide some support for the hypothesis that mothers adjust their speech directed toward children as a function of the child's language ability.