According to a report by the TheAssociated Press, the child has been hospitalised, and his father detained.

A neighbour heard "sounds of a child'' coming from a van on Monday in the village of Hagenbach near the borders of Switzerland and Germany, AP quoted a statement from Prosecutor Nicolas Heitz provided Saturday.

The police forced the van open and found a child "lying in a fetal position, naked, covered by a blanket on top of a mound of trash and near excrement", the statement said.

The child is malnourished and can no longer walk after being in a seated position for a long time.

The boy's father told investigators that he put the child in the truck in November 2024 "to protect him", because his partner wanted to send the boy to a psychiatric hospital, the prosecutor said. The boy was 7 at the time.

The prosecutor, however, said there are no medical records proving that the boy had any psychiatric problems before he disappeared, and that the boy had had good grades in school.

The boy told investigators that he had "big difficulties'' with his father's partner, and thought his father "had no choice" but to lock him up. He said he hadn't showered since 2024.

The father has been charged for kidnapping and other offences, and kept in custody. His partner denied knowledge that the boy was in the van, according to the prosecutor. She was handed preliminary charges, including for failure to help a minor in danger, and released under judicial supervision.

The boy's 12-year-old sister and the 10-year-old daughter of his father's partner were put in the care of social services.

The prosecutor's office is investigating whether others were aware of the locked-up boy. Friends and family told investigators they thought the boy was in a psychiatric institution. His teachers were told he had transferred to a different school, according to the prosecutor's office.

Authorities did not release the names of the victim or family members.