The researchers have pinpointed a rearrangement of DNA present in around two-thirds of all cases of the most common brain tumors in five to 19-year-olds.
The most common type of brain tumor is pilocytic astrocytomas.
According to the researchers, the discovery could pave the way for creating better treatments and make diagnosis more accurate.
"If we can diagnose exactly which type of brain tumor a child has as early as possible, the tumor is more likely to be treated successfully," the Scotsman quoted Professor Peter Collins, who led the research at Cambridge University, as saying.
"We also hope the findings will mean it is possible to create therapies in the future that block the activity of the fusion gene and halt the growth of tumor cells," he added.
"This is the first time a specific genetic link has been made to the majority of pilocytic astrocytomas.
"We found a specific rearrangement of DNA in around two-thirds of all cases of pilocytic astrocytoma. The resulting DNA sequence includes a portion of a gene called BRAF that is known to be mutated in a number of other cancers, and which we think may trigger this disease," he added.
The new study is published in the journal Cancer Research.