Showing that love is not always patient or kind, the parents were led into temptation after a disagreement over visiting church on the day of the Lord.
They stopped in a car park on the road to Freiburg, in the south-western state of Baden-Württemberg, and left their son there on Sunday because he did not want to go to church.
"The child thought it was a joke but that proved to be the wrong assumption when the parents in fact drove off and left him behind in the car park," Freiburg police said in a statement on Sunday night.
A witness, thinking the parents had forgotten their son, called the police. Officers picked up the boy minutes later and brought him to a youth welfare centre in nearby Titisee-Neustadt.
The father was told about the location of the son around 11am but the parents did not pick him up until 6pm.
Police are now investigating what exactly happened.
The letter of the law
Neglecting parental duties can be a criminal offence and prosecutors signalled there would be no forgiveness for the parents.
"When a child is left behind on a national road, it seems fairly clear that there is a violation of the duty of care," said chief prosecutor Michael Mächter.
If the two are found to have grossly neglected their duties, they could face a fine or up to three years behind bars.
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