A former young South Australian of the year finalist has admitted to child sex charges.

William Russell came before the District Court on Tuesday and pleaded guilty to communicating with a child to groom them for sex.

The Advertiser said Russll pleaded guilty to grooming an underage boy, who cannot be named for legal reasons, in July 2017.

Russell was remanded on continuing bail to return to court in September for sentencing submissions.

The 24-year-old had previously admitted to other charges, including possessing child exploitation material.

He was a finalist in the 2016 SA Young Australian of the Year Award for his advocacy work to help protect young people online.