Is it just me?

Are you using MCCC by chance? The settings for that will kind of override the traits, at least in my experience.

That's most likely on MCCC, townies in the vanilla game don't reproduce, the population is just replaced by cloned randoms within 2 generations.

I am using MCCC but never had it go crazy with babies and kids like this before. (focused on one trait)

Mccc story progression is random but i believe there is a setting that exclude specific traits.

Before I was using MCCC I'd seen it happen more, but with my settings using the mod I haven't noticed it as much. I have to agree that many "good" sims aren't good, I've even had them with no mischief auto go to troll the forums, seen angelic toddlers make a mess, I think those should not happen if you really are good or angelic

And that's the problem with traits, they have no real impact on the sims. They will troll teh forums, make messes, cheat on their partners and, in my current household, want to sneak himself to a winterfest gift. Although that's also a case of wanting to do something a trait is preventing him to do (whims are also broken in many cases, like children wanting to make drinks or do tv-workouts).

I have MCCC set to no autonomous flirting, unless the target is the spouse. If Nancy has a baby, Geoff will absolutely be the father, and he will also not impregnate anyone else but her. For all I know, YOUR Geoff don't even know those girls or they've only met briefly so they're on his relationship panel. MCCC may still use him as a "donor" of sorts. I've only played one guy who had a child that way, and he barely knew the mother. I don't know, really. I only know that MCCC can wreak havoc on a save if you don't set it up how you want it, or change things you don't want it to do. I've had saves where every premade household had their single sims move out on their own, and other households were totally split up, like the Caliente, PartiHouse and the Behr's. You'll quickly run out of real estate that way :#

Unplayed single females will also some times have a baby, if they are a valid target for MCCC pregnancy. I've had as many as 20'ish single mothers in a save (so sometimes I make a big house for them or edit and use one of the prebuilt large houses, and move them in together).

I have MCCC too and it definitely does not take traits into consideration. One of my sims who was supposed to be unflirty had six kids with three different women thanks to MCCC.