Central nervous system (CNS) tumors represent the most frequent solid tumors among adolescents and children, and the leading cause of cancer-related death in men < 40 and women < 20 years of age. Brain tumors are challenging to diagnose, monitor, and treat. The current diagnostic approach involves magnetic resonance imaging (MRI), tumor histology, molecular characterization and cytologic analysis of cerebrospinal fluid (CSF). However, surgical procedures pose potential risks to the patient's health, not achieving good accuracy. For these reasons, it is crucial to identify new non-invasive disease biomarkers to improve patients' stratification at diagnosis and during follow-up and prognosis. MicroRNAs (miRNAs) are a class of short RNA molecules that have been demonstrated in numerous studies to be dysregulated in brain tumor patients. As a result, they may be used as biomarkers of brain tumors. Additionally, miRNAs can be analyzed in liquid biopsy samples, such as blood and CSF, providing a non-invasive source of biomolecular data on patients' disease status. This review aims to highlight the role of miRNAs in liquid biopsy, also known as circulating miRNAs, as potential non-invasive cancer biomarkers in both adult and pediatric populations and to suggest their potential impact on clinical trials.