Aim: To explore the validity and strength of evidence on the association between environmental factors and risk of developing childhood (0-14 years) cancer. Methods: An umbrella review was conducted including systematic reviews and meta-analyses of observational epidemiological studies that examined the association of any environmental exposure of either parent or child with any type of childhood cancer. PubMed and Scopus databases were searched until April 2020. Based on predefined criteria, the evidence was graded into strong, highly suggestive, suggestive or weak. Results: 509 meta-analyses explored environmental exposures and risk of developing 10 different types of childhood cancer. Only 2.4% of the associations were considered to have highly suggestive evidence inferred by strongly statistically significant results. These associations were confined to increased risk of overall leukemia, especially acute lymphoblastic leukemia (ALL), in relation to high birthweight, paternal smoking and exposure to pesticides, particularly insecticides. By contrast, maternal multivitamin supplementation during pregnancy (summary odds ratio [OR]: 0.64, 95% confidence intervals [CI]: 0.52, 0.80) and breastfeeding for more than 6 months (summary OR: 0.76, 95%CI: 0.68, 0.84) were supported by highly suggestive evidence for decreased risk of ALL. There was also highly suggestive evidence for increased risk of central nervous system (CNS) tumors, especially astrocytoma, in relation to high birthweight, as well as increased risk of testicular cancer in relation to testicular microlithiasis and isolated cryptorchidism. Conclusions: The present findings provide evidence that exposure to seven maternal/neonatal factors significantly affects the risk of childhood leukemia, CNS tumors and testicular cancer. Further evidence from sufficiently powered studies and large consortia with uniform reporting of analyses is needed to allow firmer conclusions to be drawn.