Base game only, no mods.
Got a notice to celebrate the birthday of the older infant in a 4 person household consisting of father (at work), mother (pregnant for third time) and two infants. Mother has repeatedly tried to plan the birthday party, but "No one in the household is having a birthday today." To eliminate possible variables, the mother has sent Grim home (who she had summoned with the Grimophone to talk about grilled cheese) and dismissed the nanny (who was still in the house helping after being hired about two days before to watch the older infant while the younger was born in the hospital, but that's a separate bug) and repaired the game.
I know the mother isn't eligible for a birthday party due to being pregnant, but it seems the Plan a Social Event logic isn't recognizing infants as being eligible for birthday parties, despite them being able to be chosen as the birthday sim in the next step. I presume I'll be able to plan the birthday party once the father gets home from work.
Addendum: Sure enough, once the father returned from work, the mother was able to plan the birthday party for the infant.
Edit By crinrict: Adjusted Title to fit old bug report.
