Other than idle curiosity of any supernatural qualities of the babe, not much. And I'm wondering, is Dawn "real" now? That is, if she dies then does the baby (or who she grows into) fade from this reality, and all memory of her?
Since this was posted in the Xander forum I presume this is actually asking about Xander having sex he knew from back when she was a child. Even if I took the comics seriously, I wouldn't care. He knew her then, and he knows her now, presumably a kick-ass woman both smart and resilient, courageous and...what's the word? Extraordinary. He's always liked women like that. It would be a huge leap in my mind to think Xander is just imaging Dawn when she was 10 every time he was with her, and if Xander really was perving out like that, then surely Dawn and/or the supernatural friends of Dawn realize it given how perceptive they have to be (plus psychic senses some have).
Guess it's worth mentioning that the reason I consider the sexual consent of minors (with adults) to be invalid is for the same reason I consider their signature on a contract to work for a sweat shop or join the military (even at an older age) to be invalid. They're simply too vulnerable to the tricks and manipulations of adults (though raising them in a bubble as so many do only exacerbates that). That's generally speaking, of course, but as that's the way to bet, I support the prohibition against giving consent (and I say that wishing I had power over myself at age 14, and still believe I'd have made better decisions for myself in a court of law than my own mother).
Puritanism, or looking for a reason to declare a guy a predator, just doesn't factor in for me here in any way since Dawn is of age, and furthermore, Xander never showed any interest in her in that way during the TV series. I'm just glad that, going by Anya, Dawn has a skilled lover (told you I'm not a Puritan) who, I'm sure, genuinely loves her, will provide for her (and not be threatened should Dawn end up making more money than him), and would die protecting her.