BioMarin received the voucher when it got approval of the drug Vimizim, for a rare pediatric disease called Morquio A Syndrome. Regeneron and Sanofi said they'll apply it to get a faster review for a cholesterol drug in development, in a class in which they're in a tight race with rival Amgen.
Though Morquio A isn't cancer, the sale showed the program's working, Goodman said. Still, there's more work to be done. Dana-Farber's Sallan points out that most drugs are tested in children only after the medication has been proven to be safe and effective in adults.
"That brings one of these new drugs to a child usually three to five years after it's started downstream in adults, which is just fundamentally, I think, not necessary and probably not right," Sallan said.
Drugmakers may be concerned that a side effect seen in a small study in pediatric cancer could derail an entire program for a much broader adult market, Sallan said. But, he noted, "children are more resilient to the vast majority of new drugs than are adults."
Read MoreWhere we stand in the fight against cancer
He suggested companies should test drugs in children alongside adults, establishing safety first in older patients and then extending the medicines sooner to kids. He said regulation could help, by protecting companies from the risk of a child having an adverse event that could affect a drug's entire development program.
Such potential changes are especially important as cancer changes from being defined by its location in the body—lung, breast, prostate—to one based on its underlying genetic characteristics.
Drugmakers say they're looking at the issue. Genentech, owned by Swiss drugmaker Roche, created a pediatric oncology drug development team in 2012, focused on addressing kids' cancers. The group, of 25 people, looks at the science driving cancers and determines whether tumors affecting kids could potentially be targeted by its drugs in development, said Raphael Rousseau, who heads the unit.