I am just watching the fifth series of "Dexter" so beware of spoilers if you like the show. 

What struck me - compared to Sherlock - is this: 

Dexter works as a blood splatter specialist for Miami police. He has become a single father after after his wife has been murdered (!) And you know what? They actually managed to integrate the child into the story. There are problems with the babysitter, Dexter being anxious about the mental health of his son who was found at the murder scene (but probably too young to realise what happened), he somehow has to cover work and private life ... They did exactly what Mofftiss did not - show what life for a single father looks like. Having a baby that is more than a plot device but part of the story. Of course you cannot compare the shows as such but I find it interesting how differently they are dealing with a baby as a character. Btw, they even use the same baby every time (or twins), as a viewer you can relate to the child, you get to know him, see him getting older. And they use a real baby, too, not carrying a doll around. 

I think this shows that Mofftiss were never really interested in Rosie. They just used her as a plot device (that was not in Canon) and then did not know what to do with her.

And I am still wondering why they introduced a character that was not in Canon, i.e. for which there was no need, and then did not make use of her. Molly is not Canon but she is important. She does not have many scenes but when she appears, she leaves an impression. To me the only reason for Rosie Watson's existence is that she keeps John from leaving Mary. Which is not the best reason to introduce a child into a story. 

I agree that she's a plot device rather than a character.  My guess is that they wanted Sherlock's deduction and the "three" to be about pregnancy.  I think the other reason for including her is that it adds drama: I think the same reason they make the characters clients instead of it being a new unknown person every time.   There's no reason that they have to stick to canon: I'm not sure why people keep saying that they can't/shouldn't do xyz because of canon!  This isn't the Jeremy Brett series.   But anyway, they may continue to use Rosie for dramatic purposes in the future, perhaps even having her as the client (they've done very well with their use of child actors, so it's a possibility).   And Sherlock still has his vow to protect her.  

I think what they've shown in S4 is that a child doesn't need to get in the way, as far as they're concerned. 

Liberty wrote:

I agree that she's a plot device rather than a character.  My guess is that they wanted Sherlock's deduction and the "three" to be about pregnancy.  I think the other reason for including her is that it adds drama: I think the same reason they make the characters clients instead of it being a new unknown person every time.   There's no reason that they have to stick to canon: I'm not sure why people keep saying that they can't/shouldn't do xyz because of canon!  This isn't the Jeremy Brett series.   But anyway, they may continue to use Rosie for dramatic purposes in the future, perhaps even having her as the client (they've done very well with their use of child actors, so it's a possibility).   And Sherlock still has his vow to protect her.  

I think what they've shown in S4 is that a child doesn't need to get in the way, as far as they're concerned. 

It is a question of getting in the way or not to me. It is a question of creating a character and then completely neglecting her.
Take TLD: John mentions he has to get Rosie after work. He then stays away all day with Sherlock. Mrs Hudson and Molly are busy as well. He never collects his child. So where is she? It may satisfy other viewers but to me this is sloppy storytelling which I find frankly disappointing. 
 

I don't think they've ever bothered too much about realism.   And I think it's just something that we/they don't really want to have to think about.   I can't imagine it would be easy for John going on cases with Sherlock when he's working as a GP: does Sherlock only work outside of John's GP hours?    We don't know how it's managed, but it doesn't really matter as it's not relevant to the story. 

It's possible, although I think the story of John grieving and rejecting Sherlock through grief has been done.   I think her death would have to serve a purpose for the story, other than just removing her from the show.   Which makes me think they'd be more likely to just sideline her (nanny, boarding school, etc.) as they did in S4.   I could imagine her being in peril, though.  And I also feel that now they've got her, they might as well use her and make her part of the story.

I disagree.
Not that I watch them! But I seem to remember when I did, any kids in soaps are often quite glossed over.
It wouldn't be like Harry who we never see.
We have seen Rosie quite a bit already and we may occasionally see her again, or she could just be referred to.
It wouldn't have to be a nanny, a doctor(if he still doctors) can afford a child minder.

Ah, this thread. It's a comfort to find my thoughts echoed here (and articulated so well)! Either there was some level of advance planning behind the inclusion of baby Watson in the dramatis personae, or the writers wearied of scrabbling around for a suitable episode title and impulsively decided to call it the Sign of Three and throw in a surprise pregnancy at the last minute. Problem is, neither alternative is without precedent. Advance planning would mean the continued insinuation of the gay subtext as has been mentioned previously. And if I remember correctly, the now legendary dialogue in the pool scene was a last-minute addition to TGG; I wouldn't be surprised if it turns out TSOT was called something else until Moffat thought of this cleverer twist, and given their production schedule they just rolled it out and swept potential problems under the carpet until next season.

Yes, it does add something extra.  It also kind of gives a reason for John to think of straying when he otherwise wouldn't (dissatisfaction and stress of parenthood).  But I kind of like the idea that Rosie initially came about because they wanted that punchline and title in TSOT.   I don't see anything wrong with them coming up with that and then writing around it.  A bit like "what if the secret brother was a secret sister?"

I'm not convinced that she was added to give John a reason to stay with Mary, because IIRC, that's never mentioned.  It's not made a thing of.  Whether he stays with Mary or not seems to be about his relationship with her, rather than about the child.   In the end we see how desperately he loves her too, and it seems that a baby isn't needed.  

I honestly don't think they had enough time together.  They would have worked things out.
Rosie was just a bonus.