Say in WWII, the nazi's stole some valuable art from a jewish family and it ended up the position of some german family who passed it down to their kids and the

Say in WWII, the nazi's stole some valuable art from a jewish family and it ended up the position of some german family who passed it down to their kids and their kids. Now descendants of the family that were robbed find about who now has that art and wants it returned. Do they have rights to it seeing as how they were not the ones who were robbed? This appears to be the logic here. Current law says it has to be returned. But how many generations have to pass before it becomes like the land taken from indigenous populations?