What is the significance of 'Daddy Big Ears'?

Tony's discovery of a photograph in which a boy can be seen wearing Oliver's scarf, leads him and former detective Julien Baptiste to a house in Chalons Du Bois where they learn that the owners were on holiday in July 2006, at the time of Oliver's disappearance. Julien concludes that Oliver must have been brought to the empty house.

Down in the basement Tony finds an image on the wall that is all too familiar: 'Daddy Big Ears'. This is Ollie's depiction of Tony, and it’s a picture that he draws in the car when the family first arrive in France. Oliver calls it "Daddy Big Ears".

Tony is left stunned by this discovery, and it confirms Julien’s suspicion that Oliver was taken to this house when he disappeared. The question is who took him there and why?