Tumors and developmental anomalies arising in the pediatric population are rare, or even considered as orphan diseases, and childhood solid tumors may rarely be encountered in the adult population. Increasing evidence essentially based on adult-type tumors occurring in children, or in adolescents and young adults, however points towards differences in terms of biological behavior, prognosis, and response to treatment according to the age groups, thereby suggesting the existence of distinct age-related categories of diseases. Therefore, not only better characterization, but also comparison between different age groups will allow better understanding of these tumors, and of their similarities or differences. A unique feature of pediatric embryonal or blastemal tumors is their striking resemblance to developing tissue or organs, albeit at various embryonal or fetal stages. Blastemal tumors may show heterologous differentiation, in accordance with an early pluripotent phenotype: for instance osteoid/bone formation may be seen in hepatoblastoma. Developmental pathways as well as developmental anomalies therefore provide insights into pediatric tumorigenesis. Conversely, the genetic landscapes of pediatric tumors may help delineate the various contributions of deviation from normal development pathways, or lineage specification. Molecular characterization of these rare pediatric tumors is underway. Despite similar morphological findings, pediatric tumors may show divergent biological behavior according to their molecular signature and to the patient age group. Therefore, molecular analyses should be strictly correlated to morphology, and to the multiple lines of differentiation displayed. Our group is involved in the study of both developmental anomalies and tumorigenesis, with a special focus on liver pathology. In particular, we studied the anomalies of the biliary tree development in the setting of Alagille syndrome, the generation of hepatocyte-like cells to replenish the liver in inborn errors of metabolism, and hepatoblastoma, a rare embryonal primary liver tumor. By the study of the molecular mechanisms and pathways underlying normal and abnormal development and further comparison with their counterparts in tumor development, we provided insights into developmental pathways, and opened perspectives into personalized patient treatment.