This is a phase 1 open-label, single-administration of gene therapy agent AAV9/CLN7, administered intrathecally into the lumbar spinal cord region of pediatric patients with CLN7 Batten disease. This study consists of a one-time injection of AAV9/CLN7. There are two Cohorts with a low dose and a high dose. The primary objective for this clinical study is to evaluate safety. The secondary objective is to determine the efficacy of AAV9/CLN7. The secondary outcome measures include motor, cognition and intelligence assessments. The exploratory outcome measures include visual impairment assessment, cognitive evaluations, Brain magnetic resonance imaging (MRI), electroencephalogram (EEG), electrocardiogram (ECG) and echocardiogram (ECHO).