Hi FrauSchnarf. This usually occurs because there is something blocking the path between your little person and where they need to go, in this case the washer.
The most likely cause is furniture or other decor items that you have placed in the house. Even if it looks clear to you, they might think it isn't. Our little family members can be pretty picky about what "clear" means! In this situation, try moving the furniture around, especially between the sock on the floor and the washer, as well as around the washer.
Once your little people "see" a clear path, they will happily take the sock where it needs to go.
I hope this helps.