The acoustic properties of infant-directed speech (IDS) have been widely studied, but whether and how young learners' language development benefits from individual properties remains to be confirmed. This study investigated whether toddlers' word processing was affected by tone hyperarticulation in the IDS of a tone language. Nineteen- and 23-month-old Cantonese-learning toddlers completed a familiar word recognition task and were tested (a) in the hyperarticulated-tone (HT) condition in which the tonal distances were exaggerated, and (b) in the non-hyperarticulated-tone (NT) condition with smaller tonal distances that resembled those in adult-directed speech. The 19-month-old toddlers performed significantly better in the HT condition than in the NT condition, while the 23-month-olds performed comparably well in both conditions. These findings suggest that tone language learners' word recognition can be facilitated by tone hyperarticulation in IDS, in the middle of the second year of life; as their language development proceeds, this facilitatory effect appears to largely diminish by the end of the second year of life.