This is straightforward: Growing Together features an Infant Quirk called "Little Babbler" (internally: "Talker") which seems to work perfectly fine, but is never naturally generated by loot_Infants_AddElements (though it can be assigned via a cheat or the cheat menu). This seems to be an error, since instead of Little Babbler, the list of possible Quirks includes "Self-Soother" twice. In the list of blacklisted traits further down the file, "Talker" appears directly below Self-Soother, so this seems to be a copy-and-paste error.
This is a one-line fix and should be easy to patch. This error was reported twice on the old forums, but without any technical info, so hopefully this helps. For the time being, I've created a mod that restores the Quirk:
https://www.curseforge.com/sims4/mods/little-babbler-dummied-infant-quirk-restored
Edit By Crinrict: Adjusted Title fit migrated bug report: [ARCHIVED] [GRO] Infants never get Little Babbler quirk | EA Forums - 11717103
Archived thread had around 5 me toos
