I. Estimate the rates of objective response observed prior to disease progression during the first four courses of treatment with bevacizumab and irinotecan hydrochloride in pediatric patients with recurrent, progressive, or refractory malignant glioma (Stratum A [closed to accrual as of 4/21/2009]) or recurrent/progressive/refractory intrinsic brain stem glioma (Stratum B [closed to accrual as of 4/21/2009]).