Inclusion Criteria * Age from 3 to 9 years (Child) * Molecular genetic diagnosis of the CLN5 gene * Confirmed clinical diagnosis of CLN5 disease * Impaired motor and/or language function and/or impaired visual acuity * Written informed consent from parent or legal guardian and assent from study participant, if appropriate * Able to comply with protocol required assessments (laboratory sample collection, lumbar puncture (LP), nerve conduction studies (NCS), magnetic resonance imaging (MRI), etc.), which may require sedation or general anesthesia * Able to walk with or without assistance (assistance may include a walker, braces, or with one hand held) * Agree to reside within a 1-hour drive of the study site for at least 6 months following treatment (or a safely drivable distance for the study participant and caregivers according to investigator's discretion) Exclusion Criteria * Has another neurologic disease or illness that may have caused cognitive decline before study entry * Known pathogenic or clinically suspected variant in a seizure associated genetic mutation besides CLN5 * Any active infections or severe infections within the 30 days prior to study treatment administration * Presence of a concomitant medical condition that precludes intracerebroventricular (ICV) injection, lumbar puncture (LP), or use of anesthetics needed for study-related procedures * Presence of any concomitant medical conditions that preclude intravitreal (IVT) administration * Has status epilepticus that lasts longer than 5 minutes or having more than 1 seizure within a 5-minute period, without returning to a normal level of consciousness between episodes within 12 weeks before study treatment * Total anti-AAV9 antibody titer greater than 1:400 * Any anticipated need for major surgery in the next 24 months * Participation in an Investigational New Drug, Investigational Device Exemption, or equivalent clinical study in the past 6 months * Any prior participation in a study in which a gene therapy vector or stem cell transplantation was administered * Participation in other investigational studies and non-interventional studies that have similar study assessments as this protocol while the study participant is enrolled in this study with the exception of sister studies sponsored by Neurogene * History of or current chemotherapy, radiotherapy, or other immunosuppressive therapy within the past 3 months * Use of prohibited medications * Immunizations of any kind in the 45 days prior to study treatment * Requiring daytime or nighttime ventilatory support at the time of Screening * Any item which would exclude the study participant from being able to undergo brain magnetic resonance imaging (MRI) according to local institutional policy * Known allergies or hypersensitivities to the required immunosuppression regime