So, enough ado, here's the new one; sounds fascinating:
I am trying to find a short science fiction story that I read as a child. I'm afraid I can't remember it's title, or the author... It basically involves a man whose wife has given birth to a child and when he visits her, he is horrified to find that his 'son' is actually a pyramid, with tentacles instead of arms. The doctors christen the child 'Pi' and work out that it must have slipped into our realm from another dimension.
In a nutshell, in order to live together as a family, the husband and wife agree to be transported to Pi's dimension, where they will all appear as normal human beings to each other, although in reality they will take on forms like Pi's.
EDIT: It's "Tomorrow's Child" by Ray Bradbury, which can be found in his I Sing The Body Electric collection. Many thanks to squirrel_monkey