I play apartments a lot, but Birthday Parties no...Mix both together, you get some wondering...

My child is ready to become a teen, but I'd like to age another child on that same lot, who lives in another unit. Maybe some other child/children from elsewhere in the 'Hood too.
I know this is possible, with the birthday party scenario..right?
I am having a hard time inviting them though, because children don't seem to be allowed to throw birthday parties..and her dad doesn't know them! 0_o

What are my options? How do i go about..and do I need to..yeah?
Exactly.

The aging-townies option is not tied to birthday parties, but is a Freetime thing. Any time a sim ages, regardless of whether you threw a party or not, you should be getting a pop-up giving you a list of all the townies in the same age category the sim knows, and asking you to choose up to three to age along with. They don't have to be present, and they don't have to be friends. When aging townie kids to teens you'll need to use an editing tool to give them proper aspirations, or they'll retain their "grow up" aspiration.

But if the kids you want to age up are in the same complex, they're playable, and not eligible for the feature anyway. If you want them to age up, you'll have to play them at least long enough to use an aging cheat.

If you throw a party on an apartment lot, other residents of the same complex won't show up even if invited, unless it's a Building Party.

Any time I want a sim at a party but am not allowed to invite him for some reason, I deploy my teleporter cat. I don't know if teleportation would override the tendency for apartment neighbors to wander back into their own units or not.

Ok. Thank you Peni.
Any idea why I never get the pop up message, asking me if i want to age other sims anymore?
Wait..Could it be that I just don't have townie children/teens?? Only adults and young adults (since mod that allows YA to flee off campus)
How'bout that...

You should get it when adults age to elders, too.

Yes..I'll have to wait and see. It's been long since I played a family long enough to see this happen. I have real life mod.
Thanks for all the precisions. I was obviously misled.