This study will enroll 32 patients under age 21. The primary goals of the study are to determine if there is a difference in the 2-year survival rate of patients treated with radiation alone and those treated with radiation followed by PEG-Intron(Trademark) and to define the toxicities of PEG-Intron(Trademark) in the study doses. Secondary goals are to evaluate various magnetic resonance imaging (MRI) techniques for noninvasive monitoring of changes in the brainstem and to evaluate neuropsychological function.