Happily inspired by this thread (http://www.modthesims.info/showthread.php?t=616291), I thought about the possibility of adults being carried by another adult. I figured it would be easier and more plausible to use the toddler animations as some sort of base. Before I attempt to try this out, I have a few issues. 1). I can't find the animations where the toddler is being picked up. 2). I'm not so sure if the carried Sim is going to stay in the adult's arms. 3.) I'm not sure if the adult will move around with the Sim they're carrying 4). I'm not sure if Sims would go back to normal when being put down by the carrier.

Saw that thread too, looking forward to see the results and seeing what they come up with! Maybe in the future it could be expanded to things like a sim carrying a small dog or something. Anyways to your questions:

1) I think those are in the FullBuild0.package in your sims 3 > GameData > Shared > Packages > FullBuild0 folder. If you use S3PE, filter by CLIP Tag and files that begin with a2p_,you'll find files like:
a2p_idle_carry_idle2_y
a2p_idle_carry_idle2_x
a2p_pickUp_x
a2p_putDown_x
a2p_putDown_y
a2p_carry_chat_loop1_x
....and more (these are just some of them related to carrying behavior)

2-4) I'm not sure either, haven't really done any coding with postures.. but assuming they've finished their mod and skydome creates a custom interaction. Maybe its as simple as changing the age restriction in the ITUN file, and just providing additional animations that are prefixed by a2a and creating an override animation. At least that's how most interactions in the game work.

If you want to have adults be able to carry adults, you'd export these clips:

a2p_carryPose_x
a2p_carryPose_y
a2p_idle_carry_breathe_x
a2p_idle_carry_breathe_y
a2p_idle_carry_breathe_unslotted_x
a2p_idle_carry_breathe_unslotted_y
a2p_pickUp_x
a2p_pickUp_y
a2p_putDown_x
a2p_putDown_y

And you'll need to convert all these animations into a2a, but it'll be a big job, since the adult might look funny being held e.g. they might be floating above, down, out of place etc. that's what I did with mine, I made all custom animations for all of those.

Once you've got that done, you'll need to find a few files in the gameplaydata.package, but first copy that whole package to your desktop or wherever you want it. You'll also need to look for an Xml file I think called Idles, you'll copy that, paste it in a new package, then add the a2a_carryPose_x and y, also put in the idles there too.

And for others, such like pick up ITUN file, add the pick up and put down animations there. I don't think you'll need to change the age restrictions since there's already a A there.
But I do have to say, I'm not sure whether this'll work or not, since the target is for toddlers, but it's worth giving it a try, you never know if it'll work or not.

Thank you so much! I had such a hard time trying to find them. I like the idea of Sims carrying small animals! Yeah, maybe! It's worth giving it a shot to see what it can do.

Thank you TheSweetToddler! I'll call this...an experiment! Lol, I don't want adults moving hysterically XD

Haha I know! Well, good luck with it

Thanks! :D

But I thought sims could already carry small animals? I think they can actually, my sim was holding a small dog once, even a child could too.

Ah I didn't know that. I guess I don't play with small dogs enough... Btw I saw this picture of what seems to be an adult carrying an adult, if you can find this animation somewhere, maybe it could just be reused for the carrying animation:

Wells, it's okay

Sorry, there's no animations for adults to hold adults, I've looked, and there's none. That in the picture is a sim leaping into the other sims arms, it's a romantic interaction they play. Still, if you want to look for it it's probably something called "a2a_soc_romantic_leapIntoArms_x or y" something like that, animations usually tend to be named after the name in the queue or pie menu.

Thanks! I'll see if I can find it.

Lol I forgot myself XD I like the jump in arms! I want to see if I could split it in half and make one for pick and put down.