There are some races where the absence of kids can be explained away.
* Argonian kids might be more reptilian or amphibian than advlts. Maybe they can't survive in Skyrim.
* Khajiit can't enter cities. So they might leave their kids at home.
* And there's hardly any Bosmer around.
Only Khajiit caravans are forbidden to enter the cities, not indivdual Khajiits. (Most of the ones who don't belong to caravans seem to be thieves, assassins or random hostile NPCs, though.) Agreed though that they probably wouldn't bring their kids on the trade caravan. Some might be born however. They are gone for a pretty long time, and there are both men and women on those caravans

As for the Bosmer, one Bosmer woman (and a man of any race) is enough to make a Bosmer kid. There are at least four named female Bosmer NPCs, maybe a couple more I don't recall right now. One is even married (to a Nord).
I think a dialogue option, "We should have a child", would be good, but I really don't want to see six in TES. The Elder Scrolls have a certain... Class, that you don't find in Fable or other games.
Well, I presume my married characters have six with their spouses even if no kids are made

(Actually, I presume my unmarried characters have six sometimes as well. Most advlts have.)
But I agree that we don't need to see it. It would most likely be either ridiculous, or awkward, or both.