Rome/Berlin - A hunt was on in Germany and Italy on Wednesday for a German couple who abandoned their three children at a pizzeria in northern Italy, officials said Wednesday.

Two boys, aged ten months and six years, and their four-year-old sister were found unsupervised on Sunday evening at a restaurant in the town of Aosta.

The 26-year-old mother and her 24-year-old companion told the children they were going outside to smoke a cigarette and have not been seen since.

The family had arrived in Aosta on Saturday and checked into a hotel. "They looked like the typical young couple with their pretty children," hotel owner Ezio Gevroz said.

"Only when I discovered on Sunday that their credit card was empty, did I have doubts," Gevroz added.

The police later found out that the missing couple had left their car near the Aosta motorway exit, after it had run out of petrol. The family had been travelling without luggage.

"It seemed strange to me on Sunday evening," Gevroz said. "The children were dressed far too lightly, they went to the pizzeria without jacket or umbrella, although it was raining."

When the restaurant staff realised the parents were missing, they started searching the premises, reluctant to believe they had left their children behind. Finally, they called the police.

The children have since led police officers to the family's abandoned car. There they found the mother's diary, which contained suicidal thoughts.

"From the notes we could gather that the two must have been in serious financial difficulties," Aosta's Police Chief Alessandro Carmeli said.

Italian police launched a search in the Aosta valley, focusing on its many waterways, but have found no trace of the mother or her partner, who is not the children's biological father. Officers said they fear the couple acted out of desperation.

The child welfare office in the family's home town of Olpe, 70 kilometres east of Cologne, has been arranging the children's return to Germany. They are still in the care of a foster family in northern Italy, after a hospital checkup showed them to be in good health.

Two weeks ago, the children's grandmother had alerted the police that the children had disappeared with their mother. The children's father had been convicted in 2006 of shaking a fourth daughter so hard that she died. (dpa)