I've brought the backbone to the doctor and received the weird pet. I'm supposed to see the boys playing outside the pumpkin house with the rat but they aren't there. Is there's something I still need to do or is my game broken? Is there a patch?

You have to talk to the gravedigger three times first. He will tell you sth. about his rat. Then the boys will play with the rat next time you enter the scene.

Had the same problem! Thank you!!