Police believe a baby girl missing after she was not returned to her carers in County Down was taken on a ferry to Scotland by her parents.
Sophie Anderson, who is 17 months old and is in care, was visited by her mother Lucy in Banbridge on Monday.
They were supposed to attend a toddlers' group, but did not turn up.
Police said it was understood they travelled to Belfast and boarded the 1145 BST sailing to Stranraer.
Detectives believe Sophie's father Stuart Creaney boarded the 0730 BST sailing earlier that morning.
They said they are concerned for the child's welfare and police forces across the UK have been alerted.
Sophie is described as having dark, wavy hair and was wearing a cream top with rusty-coloured flowers, cream jeans with pink flowers and pink shoes.
She may also have been wearing a yellow coat and was in a pink pushchair.
Lucy Anderson, 30, is described as approximately 5ft 6in tall with a flushed complexion, a protruding lower lip and dark, straight hair parted in the middle.
She speaks with a strong Derry accent and was wearing jeans and a grey coloured hoodie.
The 22-year-old father is described as being boyish-looking with auburn, wavy hair and a light beard.
When seen at the ferry terminal he was wearing a black coat with a red-hooded top underneath.
He was carrying a boxed TV, a black rucksack and pulling a black suitcase.
Detectives have appealed to them to return Sophie to her carers as soon as possible or contact social services, close family or police.