The start of the episode was wonderful, Robin freaking out about having children (while telling her future children about it) and Barney being thrilled to be a father. Robin's reaction to Barney's happiness was hilarious. However, when confronted about what it is really like to be a parent, and husband, Barney wants back out, and is unsure as to how it would work. Robin goes to the doctor with Barney, and they discover that she is, in fact, not pregnant, and they do a happy dance. When Robin is discussing this with her future children, she continually apologizes.
Robin goes back to the doctor the next day, or shortly thereafter, and finds out that she can never have children. She covers, but is disappointed. She never wanted children, but to be told that she never can surprisingly hurts her. With the gang, she covers, and says she can't be on the Canadian pole-vaulting team. Everyone does, to comfort her, what she imagined they would do when (if) she told them that she couldn't have children. Barney tries to tell jokes, Lily cries, Marshall tries to problem solve and Ted goes for comfort.
When they go back to help Lily register for baby gifts, Robin is somewhat distraught, and Ted assumes she wishes she could go home for Christmas, so he buys her a ticket to join him. She declines, says all that she wants is to be alone, and that is isn't his job to comfort her. He says is it, they have a sweet disagreement about it, and she decides to go for a walk, when we find out that her future children, were never her future children. She gets home and Ted comforts her with a Christmas light display to AC/DC, and his voiceover to his kids mention that she never becomes a mother, but she is a successful reporter and much more.
The secondary story of Marshall decorating and the kid taking over his house was a bit silly, but somewhat enjoyable. You got a glimpse of their new life, and how Marshall might be as a dad.
The best part of this episode, to me, was the surprise that Barney and Robin don't have kids. I'm glad. The story was a great story, slightly sad, but not the worst thing ever. I would have been disappointed if Barney had been the father, and she had been pregnant. It would have ruined the surprise of the bride in the wedding that Barney is the groom. Now, we don't know. barney could meet someone new, maybe he works things out with Robin, who knows?! And that is part of the reason we all watch the show... for the surprise. Now... can we get a clue about the mother!!! PLEASE!