This report examines spectrum-wide (1 to 100 Hz) differences in electroencephalogram (EEG) power between eyes open (EO) and eyes closed (EC) conditions in children. A high density (60 electrode) system was used to measure EEG power at 4, 5, 7, 9, and 11 years of age. Results showed spatial and frequency band differences as a function of age. Speci cally, 1) the alpha peak shifts from 8 Hz at 4 years to 9 Hz at 11 years, 2) EC results in increased power at lower frequencies but decreased power at higher frequencies for all ages, 3) the sign change for the difference between EO and EC occurs in a narrow band of frequencies which changes across childhood, 4) at 4 and 5 years, EC increases lower frequency power most prominently over posterior regions; 5) in contrast, at all ages, EC decreases power above 30 Hz most prominently over anterior regions. These results extend previous ndings to show EO/EC differences in higher frequencies and to the presence of developmental changes across childhood. This report demonstrates that the simple EO/EC task can provide important information about maturation of brain states and can be done with a very brief, minimal protocol.