Thousands of children with leukemia count on a particular drug to survive. But supplies are running dangerously low. In many cases, doctors have enough for only three weeks. CBS News correspondent Dr. Jon LaPook looked into what's behind the shortage -- and what's being done about it.

Even though 8-month-old Elena Schoneveld was diagnosed with leukemia, her devastated parents were hopeful.

"The fact of the matter is it's curable," her father Mark Schoneveld explained. "There are a lot of cancers that are not curable. So, in regards to leukemia, we feel -- in a weird way -- lucky that they have a track record of curing it."

The cure depends on a cocktail of chemotherapy drugs. But, one of the crucial medications, methotrexate, is running out.

"Children will die because they can't get methotrexate," Dr. Jon Maris said. He is the chief of oncology at the Children's Hospital of Philadelphia, where Elena Schoneveld is being treated.

Maris explained that methotrexate is a lifesaving drug and a known curative agent when injected into the bloodstream. It is one of the main medications credited with preventing leukemia cells from infiltrating the spinal fluid.

However, the Children's Hospital of Philadelphia only has two months supply of the medication left, and children usually take it for three years.

It's not just methotrexate that's running out. Twenty-eight cancer drugs taken by more than 550,000 patients are in short supply.

One of the main problems is that companies have a a smaller profit margin because many of these cancer-fighting drugs have become generic. Fewer suppliers are interested in making the drug, including the largest manufacturer of methotrexate, which shut down its plant last fall.

A year ago, the first of three congressional bills was introduced to give the FDA more power to deal with the drug shortage crisis. So far, neither the house nor the senate has brought a bill to the floor.

"This is a real, real crisis," Maris said.

"Unless something dramatic changes in the next few weeks, myself and other physicians and nurses on this very unit will have to look parents in the eyes and say we don't have methotrexate and the substitute is not as good. And, I am sorry," he added.