It is believed a family relative has taken the couple's two children to Liverpool on a ferry.
The PSNI has once again appealed for information about a young missing family from Londonderry.
Detectives have asked for Martin and Charlene Collins to make contact.
The couple, aged 27 and 25, were last seen together with their infant son aged 23 months and daughter aged 11 months in the O’Connor Court area of Derry at around 9.30am on Tuesday, June 9.
Detective Inspector Michelle Boyd said: “It is believed the children may currently be in the care of a female relative.
"They were sighted with her in the Northern Mall in Belfast on Friday 12 June and then again later that date boarding the ferry from Belfast to Liverpool.
“I am urging this female relative and Martin and Charlene, or anyone who knows of the current whereabouts of the children, to get in touch with police by calling 101 quoting reference 1225 09/06/2020.”