Hello, I'm Tplumbo, a newbie in modding/scripting TS4 area.
Got a bit of experience with creating custom content, posing and animating, but my real dream it's to make them "functional" in the game.
So, my actual objective is to explore the newborn sims animations, more like to make a new one. But I have no idea of how I can make that possible xD since newborn sims are half sim, half object (which I never tested animation with).

I don't know if Sims4Studio has a module for object animation/posing, my idea would be like when you click on the newborn, the pose player interaction appears.
Plus thing is that I actually found the baby rig in Sims4Studio objects library, but it only shows one skin tone/eye colour. I got the crib mesh too, but I guess an invisible crib (plenty of mods out there, not sure if I should make my own and put it into the code or collab) would be more practical.
Well, I hope someone helps me.
P.S.: really sorry for any bad English issues.

I highly recommend starting smaller and not jumping into anything related to babies just yet, as well as getting more experience with general modding first. You need to have an understanding of how object tuning, the connected tuning, and their animations work before tackling something like this. For the skintone though, the crib has those textures attached, it's just a matter of replacing it on the baby prop you extracted if you need it (this baby is a prop btw, the actual baby is attached to the crib). For the poseplayer idea, you'd have to create it a different way for a couple of reasons, mainly because of how the baby's function and also because Pose Player is mostly script. There are semi-similar ways to achieve a menu appearance though with tuning.

Here are some resources to get you started with modding, I recommend doing overrides first, then when comfortable start making basic custom interactions, take a peek at the animations in interactions while doing that. Then once you feel comfortable with that, move on to this tutorial here which covers how to make basic animated objects. Make a couple of test objects, study some regular EA objects, then when you feel at least semi-ready, go back to the baby and study it's files.

Thank you very much for the tips, I will definitely learn the basics and read the tutorials you gave me (I'm going to enter the discord too). But just in case, how do I access the real baby files? (what app, folder, directory should I use/go?)

Btw I'm a little confused about the python script because the newborn is half sim, half object.
That way, in addition to the tunings, you'll have a sim's python script included in the same file. I could be wrong, but I think object tuning might not work because of this issue, since adult sims can pick the baby and do direct interactions. I'm comparing this script with the pet script, pets are basically sims that have the controller disabled originally (just like babies). The problem is that pets are "alive", they are able to walk to any point of the lot, travel with the sims, be carried around and interact individually (that's why it was possible to create a mod that unlocked their control). As I understand it, babies are interactive objects that become sims when they grow, it's not like the animals in Cottage Living, which interact with the sims but don't become something controllable.
So yeah I'm hella confused

Install XML Extractor and it's companion XML File Finder. The baby's object tuning is called object_Baby, tuning id is 14826. You can use File Finder to check it's references, and if you just search "baby" in File Finder you'll get a ton of files to browse through as well.

This is what I meant by starting much smaller, so you can grasp how the game and files work which will eventually allow you to dig deeper to understand the baby. I'm not sure why you think you need a script similar to the pets (or maybe I'm misunderstanding), but the only script you need for adding interactions to objects (baby in this case) can be done with XML Injector until you (optionally) learn scripting. If your goal is to somehow make the baby standalone, not part of the crib, and independent like a pet, that's a much, much higher and difficult workload than just adding a new interaction with a new animation to the baby (there's a reason it hasn't been done yet). But objects can run their own interactions if setup right, a sim is not needed for one if you don't want it.

Got it, gonna do some basic object tuning/animation to become a script master (just like you)
And, answering your question, yep my goal was to make something like that xD. Well, I guess anything is possible, isn't it?
If it's not available yet, someday it'll be! :D