Yo, if you’re looking for hip, new tunes, check out Vault Archives, a remastering of the soundtracks of Fallout 1 & 2 by the games’ composer, Mark Morgan. Free to download, it flows through 24 atmospheric tracks, my favorite being Gold Slouch. Check it out.
If we’re talking about a general apocalypse, maybe people are more focused on surviving themselves, they don’t want to bring children into this kind of world, they can’t have children?
If we’re talking about the Fallout universe, people definitively are pregnant, we just don’t see anyone pregnant as the player. Perhaps because pregnant people would kind of stay away from the action? But most likely it’s the same reason we don’t see people with missing limbs, and scars or any body diversity - because it wasn’t put into the game.