Your child will be assigned randomly (like tossing a coin) to receive either cidofovir or placebo (an inactive substance). Neither you nor your doctor will know which your child is receiving. Your child will undergo a total of 6 bronchoscopic procedures, which involves placing a tube down your child's throat so that the warts can be seen and treated. The warts will be removed by laser or other procedures and the study drug injected. Study drug will be injected at the sites of all newly removed warts and warts which were removed during earlier study visits. This procedure will be performed every other week. Blood and urine tests will also be performed at this time. Your child will be under general anesthesia during each procedure and will be in the surgery unit for about 6 to 8 hours. Your child will also have to be seen by the doctor 2 days after the procedure. Your child will be followed for a total of 5 years to make sure he/she develops normally and to monitor any side effects of cidofovir. Follow-up visits will take place at Months 3, 6, and then once every 6 months through Year 5. If necessary, laser or other procedures will be performed at these visits to remove any warts.