• \>= 2 years and \< 18 years at the time of enrollment

• Weight must be \>= 18 kg. For patients \< 12 years of age and expected to receive cyclosporine, weight must be \>= 30kg

• Planned allogeneic HCT (bone marrow, peripheral blood stem cell, or cord blood transplant)

• Patient must be CMV sero-positive (i.e., recipient CMV immunoglobulin G positive)

• Patient is eligible for entry only if it is feasible for plasma CMV PCR testing to be sent and resulted within the protocol mandated time period

⁃ Reminder: To limit the likelihood of positive plasma CMV PCR post-enrollment and prior to start of study treatment period, it is recommended that patient enrollment proceed after patients start their transplant preparative regimen

• Patient must have a performance status corresponding to Lansky/Karnofsky scores \> 50

⁃ Note: Use Lansky for patients =\< 16 years of age and Karnofsky for patients \> 16 years of age. For further reference, see performance status scales scoring under the standard sections for protocols among protocol reference materials provided on the Children's Oncology Group (COG) member website: https://members.childrensoncologygroup.org/prot/reference\_materials.asp

• Estimated glomerular filtration rate \> 15 mL/min/1.73 m\^2 and not receiving dialysis

• Total bilirubin =\< 2.5 mg/dL and serum glutamate-pyruvate transaminase (SPGT) (alanine transaminase \[ALT\]) =\<10 x upper limit of normal (ULN) for age

⁃ Note: For the purpose of this study, the ULN for SGPT (ALT) has been set to the value of 45 U/L