Role of Genetics and Vaccinations in Childhood Cancers

The  main causes and approximate percentage of cancer deaths fall into 3 classes : Genetic-  20 % ; Smoking  25% (in males) ; Diet-35%, with the remainder due to various environmental factors like radiation. It is obvious to oncologists that in the case of the environmental causes like smoking and diet, the duration of exposure plays a significant role if and when such tumors will develop.
Not surprisingly  such tumors are  rarely found in children  suggesting that genetics may play a more significant role in childhood.
Oncologists have been busy searching for such cancer genes  and have already found several, e.g.  breast, stomach, colon and other cancer genes, adopting various preventive measures in asymptomatic children, e.g. removal of healthy organs!
 Because in children brain tumours and leukemias are more common, could their etiology still be some  environmental factor that we have not discovered? like a viral agent. These could easily be introduced with the various vaccinations our children now routinely get.
I am still uncomfortable about the pandemic of AIDS and now the  Ebola virus in Africa and elsewhere,  Some epidemiologists have suggested the west may have introduced the AIDS  pandemics with our vaccination programs for polio. I seem to recall that our polio vaccine did transmit the Simian virus 40 with our vaccination program- fortunately for us this tumor virus does not produce tutors in humans.- only in mice as I seem to recall. Could our vaccinations  be responsible for some the brain tumours and/or leukemias found in children ?