Since their discovery in 2008, cell-free circulating microRNAs have been considered potential biomarkers for various conditions, including pediatric cancer. Diagnosis of pediatric cancer still relies on clinical signs, which sometimes may be non-specific or appear at later stages. Thus, there is a need for a better understanding of molecules that allow a less invasive, early and effective method of cancer diagnosis. Despite the efforts of many researches to set specific miRNAs to be routinely used as diagnostic molecules, no miR has been currently utilized so far. In this study, we review the recent discoveries on circulating miRNAs in blood of patients suffering from the following pediatric cancers: osteosarcoma, rhabdomyosarcoma, Wilms tumor, acute myeloid leukemia, acute lymphocytic leukemia, retinoblastoma and neuroblastoma. We also focus on the roles of circulating miRs in tumorigenesis pathways, the methodological approaches used to detect and quantify circulating miRs, and discuss the challenges in using them routinely as biomarkers for pediatric cancers.