Part A: Children will receive rIL-2 intravenously for 5 days every 8 weeks for 3 cycles. The study will enroll 4 patients in each of 3 dose levels. Dose escalation may occur if all 4 patients in a dose level tolerate therapy without evidence of Grade 3 (or higher) toxicity. If 1 of 4 subjects in any dose level experiences at least Grade 3 toxicity, 2 additional patients will be enrolled in that dose level. If 1 of these 2 additional patients experiences at least Grade 3 toxicity, dose escalation will not proceed. NOTE: Once Part A is completed and the maximum tolerated dose is established, children who participated in Part A and received less than the maximum tolerated dose will be offered additional therapy consisting of 3 cycles of rIL-2 at the maximum tolerated dose.