Two young children were reportedly sent on a cruel treasure hunt by their mother and step-father before they were found crying on the side of a road in Portugal.

The French boys, both under the age of five, were found by a driver in the Portuguese town of Alcacer do Sal about 7.30pm on Tuesday.

It is believed that before they were allegedly abandoned by their mother and step-father, the boys were blindfolded and told to dig for a knife to remove their eye coverings, under the guise of a treasure hunt.

Once the blindfolds were removed, the adults had disappeared.

The kids were armed with a backpack which was said to be carrying water, fruit, biscuits and a change of clothes.

The children had no form of identification on them when found by the driver, local baker Artur Quintas.

Local media, Sic Noticias, said Mr Quintas said the children were covered in dirt and had some bruises.

“Through the car’s review mirror, I saw them coming towards me, shouting and crying,” he said.

He said they were told to “play a game” before being abandoned.

The Portuguese National Republican Guard said the children were taken to a nearby home before being transferred to a hospital.

CNN Portugal reported that the children were released from hospital into foster care about 8pm

The children were reported missing from their home in France on May 11 by their father.

Local media reported that a couple, believed to be the mother and step-father, were arrested when their car was found at a cafe about 180 kilometres north of the town.

They had reportedly been at the cafe for several hours prior to their arrest.

The 41-year-old woman and 55-year-old man have not yet been formally identified.

Portugal’s National Republican guard said they were being investigated for domestic violence, exposure to danger, and abandonment, as reported by the BBC.

It is understood the mother resided in Colmar, France, about 500 kilometres from Paris.

The children’s father is on his way to Portugal from France.