Sex Crimes Squad detectives investigating allegations of abuse on an eight-year-old girl in 1985 and two 13-year-old boys in 1987 made the arrests last night.

The 58-year-old former teacher was arrested at a Blacktown address just after 5pm and a 59-year-old Catholic Brother was arrested at The Entrance on the Central Coast an hour later.

Both were assisting police with inquiries at separate stations.

"Police encourage any victim of sexual abuse, no matter how long ago the incident occurred, to report it to their local police station," a police spokesman said.