The purpose of this study is to evaluate how ganciclovir is metabolized when administered intravenously (by a needle inserted into a vein) following valganciclovir syrup, given by mouth to newborns and young infants with symptoms of congenital (present at birth) cytomegalovirus (CMV) disease. The study also seeks to identify a dose of valganciclovir that provides a comparable blood concentration to ganciclovir present in the blood of newborns with symptomatic congenital CMV disease. All study participants will receive 6 weeks of antiviral therapy (defined as ganciclovir and/or valganciclovir). Infants from 0 to 30 days old will participate in the study for 2 years.