The real problem with this story is that there's not much story to the story. There's hardly any plot to speak of. Widower buys an electric grandma for his kids. One kid resists electric grandma. Then finally accepts her. Then the kids grow up and grandma leaves. Really, very little happens. It's much more of a premise than a story.
Moreover, strip it of it's schmaltz, and you have a story that had already done before, and better: The Lonely. Same basic idea: person initially can't accept the love of a robot, because it's just-a-machine, then eventually yields and comes to love the robot. The biggest difference is that The Lonely is much more powerful, as both the protagonist and we, the audience, are shocked abruptly back to reality and forced to remember that in the end the robot really is just a mechanism.
I also find the story highly flawed in that the electric grandmother is just *too* perfect. She's not only "human", she's *super-human*. She's *wiser* than a real person, she has no traces of mechanicalness to her at all, and she makes marbles appear out of thin air. It frankly really chafes at credulity to think that she's a machine.