I don’t understand the desire to saddle every female character with children regardless of whether they want them as some lazy stand-in for a happy ending, particularly in sci-fi and fantasies. If you’ve earned that with sufficient backstory and evidence, like, FINE. Olivia Dunham and Donna Noble and Scully and Ripley canonically want to have children. Amy Pond, Hermione Granger, Kara Thrace, Katniss Everdeen - these women are all ambiguous about or uninterested in being mothers. So it’s problematic when a head writer or a fan art illustrator or a writer of fanfiction just sticks these women with children as though motherhood is always the inevitable and right and desirable end, even when their characterization directly contradicts that.
Even River Song falls victim to this trope because that is the image Moffat chooses to close on in the Library episodes. River, a woman who has never expressed any desire to raise children or be a mother, someone who (if her arc had allowed for any emotional consequence whatsoever) would likely have had some deep-seated issues with nurturing and parentage and abandonment - is “saved” in a purgatory/afterlife where she is forever caring for these ersatz, computer-generated children. Because children are shorthand for happiness in women’s narratives.
Opening a can of worms here, but I while I am in theory not exactly opposed to what you are saying, the examples you give simply make me shake my head. Especially when it comes to River!
Silence in the Library / Forest of the Dead is the absolute first time we ever see River, but it should be the absolute last. Considering how they’re running for their lives the entire time, and she knows this Doctor isn’t her Doctor, I do not see why or how she’d bring up the subject of children. However, the computer program tends to want to keep people happy - this has been textually established - so it gives them what they want. It is safe to assume that since she ends up caring not only for Charlotte (who is an actual real person, albeit one stuck in a computer), but for the virtual children as well, that she wanted them. Add to this the fact that she knows they’re not real, and I think it’s fairly logical to assume that the idea of motherhood (in any form) did not repel her.
Considering that this is the first time we meet River, and that what we perceive as “development” is actually “backwards development”, as we see her younger and younger versions, how to we truly know? We see an older, emotionally stable River, who is in the company of a man who she knows doesn’t truly know her. He can barely bring himself to kiss her, so how and when is she supposed to talk to him about children? It would make no sense whatsoever. And then we see a young and wild River, who, when confronted with the Doctor, is too busy killing him, then too busy destroying the universe to save him. When - or why? - would she ever want to mention children? If they’re ever to be mentioned as something she wants (or doesn’t, for she’d have plenty of reasons NOT to want any), they won’t be until what we perceive as the 7th series, during her actual time with the Doctor, when they’re both n’sync enough to be able to discuss these things (if at all).
And something else… By the time she dies and is stuck in the computer, she was also most likely emotionally stable and well adjusted enough to teach at a university, so perhaps some of the wounds left by her unconventional and traumatising childhood have healed, leaving room for her to potentially consider having a family (again, something she couldn’t tell Ten, even if she wanted to). Basically, saying she will NEVER want any children simply because she doesn’t expressly say that she wants them (SO FAR!) is so ridiculous it borders on funny.
To assume that a character (or real person, for that matter) wants the same things over the span of their entire life is unrealistic and limiting. As a woman, I reserve the right to change my mind any time, as many times as I want, without having to justify myself to anyone, and I reserve the same right for fictional character.
So basically yes, I agree, it is absurd to assume that family+children=happiness (for women OR men), but at the same time it’s just as absurd to say that just because a woman doesn’t does go on and on about how she wants to be a mother she doesn’t want to become one, or wouldn’t make a good mother if given the chance.