Max and Ruby's parents are actually seen & mentioned in the series. Though you can catch a quick glimpes of them in the episode Louise's Secret where a family portrait hangs above the sofa. Many people have asked what happened to their parents but they are still living. It was said by the creator of Max and Ruby, Rosemary Wells, that they are still living but seen because she wants it to be where kids solve things on their own, but they are still living and shown in Season 6 ep1 - (none)