For years, I've been looking for a short story about a boy who discovers alien pods in a field that are growing replacement people. If I remember right, he sees the pod creature eat his mother and then become her, and no one believes him. The story ends with him going in to see his dad, one of the few real people left until that point, and seeing something (an empty pod maybe) that lets him know his dad has been taken and he's next. I'm thinking that the title was something like Father Figure, but I may be remembering wrong.
The story was part of several collections of classic science fiction stories that we had on our bookcase when I was growing up, so I'm guessing that the story could be from the 70's or any time earlier.