Wilms tumor (WT), the most common pediatric renal malignancy, exhibits a relatively low mutational burden compared to adult cancers, which hinders the development of targeted therapies. To elucidate the molecular landscape of WT, we perform integrative proteomic, phosphoproteomic, transcriptomic, and whole-exome sequencing analyses of WT and normal kidney tissue adjacent to tumor. Our multi-omics approach uncovers prognostic genetic alterations, distinct molecular subgroups, immune microenvironment features, and potential biomarkers and therapeutic targets. Proteome- and transcriptome-based stratification identifies three molecular subgroups with unique signatures, correlating with different histopathological subtypes and putative cellular origins at different stages of embryonic kidney development. Notably, we identify EHMT2 as a promising prognostic biomarker and therapeutic target associated with epigenetic regulation and Wnt/β-catenin pathway. In this work, we provide a comprehensive molecular characterization of WT, offering valuable insights into its pathogenesis and a foundational resource for future therapeutic development.