Around 20% of children worldwide suffer from insomnia. There are no approved drugs available for treating insomnia in children, and there may be treatment-related side effects. The Gamma aminobutyric Acid (GABA) is a neurotransmitter widely present in the brain, and GABA extracted by industry is a common food supplement. Previous studies indicate that oral GABA supplement can improve adult insomnia, and has the potential to reduce blood pressure, relieve stress and other effects. At present, there are few studies using oral GABA to improve insomnia in children. The purpose of the study is to explore the effects of oral GABA supplement on symptoms of insomnia (short - or long-term insomnia) in children. In this study, 206 children aged 6-12 years with a diagnosis of insomnia will be randomly assigned to receive GABA supplement of 100mg/ day or placebo for 2 weeks. Subjective and objective sleep parameters such as sleep onset latency (SOL) were measured with sleep questionnaires, diary, and actigraphy at baseline and 2 weeks later, while emotional/behavioral problems, and cognitive ability will be measured with parent-reported questionnaires. Also, related brain function was assessed with functional near-infrared spectroscopy (fNIRS). This study can provide more reference for the application of GABA in children with insomnia as a complementary and alternative therapy, and clarify the mechanism of action of GABA on insomnia.