Missing Sydney baby and parents found

A six-day-old baby boy whose welfare police had grave concerns for has been found.

Police appealed for the boy's parents to take their son to hospital on Saturday, four days after a health worker first raised the alarm.

The boy was suffering a medical condition and required assessment and possible treatment, Inspector Stuart Sweeney told reporters at Auburn on Saturday.

He is now in the car of medical staff at the Sydney Childrens Hospital, a NSW police spokesperson said later on Saturday.

"The boy was taken to hospital by a number of family members earlier this evening," they said.

His 25-year-old father was arrested at Mascot about 6pm and his 28-year-old mother arrested two hours later at the hospital.

Both are assisting police.

Insp Sweeney had earlier revealed the parents were believed to be actively evading police attention.

"We really want the parents to consider the situation that they're putting their child in," he said.

"Our concern is totally driven toward the welfare of the child and getting it properly assessed medically and treated if need be."

A health worker, who visited the family at their Smith Street home in Regents Park on Wednesday, raised the alarm when they returned on Thursday and found the family had fled.

There was an unconfirmed sighting of the baby at Little Bay later on Thursday.