Is it permissible for children intending to perform Hajj to wear underwear beneath the Ihram garments to avoid friction and chafing, especially after undergoing a testicular operation?

A child in a state of Ihram (definition) must avoid what an adult avoids, including wearing tailored garments such as diapers. These should only be worn out of necessity, and if so, a fidyah (definition) (expiatory offering) becomes obligatory, to be paid from the guardian's wealth. Inflammation can be avoided by applying an unscented ointment.