"Three middle-aged white guys get the sack.."

[SLUDGE FACTORY]

The above source as well as this Oxford Dictionary: https://www.lexico.com/definition/nonce
seem to state that the term is not used exclusively in relation to children.

A person convicted of a sexual offence , especially against a child

That suggests clearly that nonce refers almost exclusively to child sex offenders

[Rjk]

A person convicted of a sexual offence , especially against a child

That suggests clearly that nonce refers almost exclusively to child sex offenders

no it doesn't

[Taunton Blue Genie]

A person convicted of a sexual offence , especially against a child

That suggests clearly that nonce refers almost exclusively to child sex offenders

Not exclusively then.