Two men admitted on Thursday to sexually abusing children at a campsite at the start of a trial that has shone a light on horrific failings in the German child protection system.

Defendants Andreas V and Mario S admitted to almost all of the hundreds of charges of sexually assaulting young children at the trial in the western town of Detmold, a court spokesperson confirmed.

Prosecutors accuse the men of carrying out the crimes against at least 40 children over a 20-year period at a campsite near the Dutch border.

Andreas V, an unemployed 56-year-old who lived permanently at the campsite, is charged with abusing 23 young girls.

The children were reportedly friends of his foster daughter who he lured into spending the night in his caravan.

The men allegedly filmed the crimes. Hundreds of pieces of photo and video evidence were found at the men's properties.

The admissions mean that the children, some of whom are not yet of school age, may no longer have to testify in the trial which is has nine more scheduled days.

As details of the crimes have emerged since Mr V’s arrest last December, the scale of the institutional scandal that allowed the crimes to be perpetuated has emerged.