Purpose: This study investigated the development of spatial release from masking in children using closed-set Mandarin disyllabic words and monosyllabic words carrying lexical tones as test stimuli and speech spectrum-weighted noise as a masker. Method: Twenty-six children ages 4-9 years and 12 adults, all with normal hearing, participated in speech recognition tests under 2 conditions: (a) speech and noise spatially mixed and presented from the front (NF), and (b) speech presented from the front with noise spatially separated and presented from the side (NS) with different signal-to-noise ratios (SNRs). Performance-SNR psychometric functions were obtained that generated the SNR for a 50% correct score (SNR-50%) as the outcome measure. Results: In the child participants, SNR-50% improved with age in NS but not NF. The difference in SNR-50% between NS and NF--the spatial release from masking (SRM)--increased with age with an average improvement of 0.1-0.15 dB per month. Conclusions: SRM has a long developmental time, at least up to 9 years of age, which is significantly longer than some previous developmental studies have suggested. The child participants had not yet reached the adult SRM performance level. SRM is a potential clinical measure to reflect the maturation of spatial auditory processing.