Sorry to hear about your dog problem. I am sure it is stressful for all.
I have a shy/cautious sensitive heeler mix (similar in temperament & intelligence to aussies) so I know how challenging it can be with new stressful situations. Sounds like your dog possibly is stressed by all the visitors, and thus the change in your household routine. I have found that our sensitive dogs thrive on routine and tend to get pretty stressed by change or new/novel things.
I have a new pup and so I am acclimating her early on to all new-- and possibly stressful to her--- things such as: babies and their sudden noises and screams, toddlers who move fast and don't really know yet how to move safely around dogs, kids who want to get in her face and hug her and step over my dog (eeek ---unsafe!!) etc etc. Also wheelchairs, walkers, baby strollers, skateboards, bikes, you name it.
I take her to areas where kids are and I have tons of yummy lil treats in my dog treat pouch and as the kids are petting her and they are doing her many fun dog tricks, I give my dog the treats so she learns that GOOD things happen when babies and kids are around. I started by just having her watch and listen to kids playing roughly/loudly at a distance
just to be sure/safe. And I always verify that it is ok with the parents if my dog meets their kiddos.
This new pup is very good so far with kids. But my sensitive heeler dog I would not take a chance. Not worth it. I take her around kids but always manage her on leash very carefully (and gently) and do not have kiddos pet her. Nope. Better safe than sorry!
But--if your dog is reacting now by warning growls etc your dog is screaming that it is stressed or nervous. Thank heavens that your dog trusts you enough to growl and say "Hey mom/dad, I am stressed out!! Give me space or a break from this situation" You are lucky that your dog is giving you advance notice--this allows you to work on it it together. Please
be really careful and take precautions. Use baby gates to separate dog from baby. Cheap, easy helpful management tools. I have baby gates all over my house to give my sensitive dog time away from annoying puppy!!!
If it was me, I would crate train the doggie and have her LOOOVE her crate with delish bones/chew treats etc so you can send her there to give her space and quiet time away from the stress of visitors, babies, etc. Never as a punishment, only a respite. If you don't want to crate train, then perhaps designate a separate room or space with a baby gate and make that your dog's safe place.
Give your dog lots of safe chewie items to chew since chewing relieves dog stress... and keeps them busy so not so worried about what is going on. Especially if you are adding more babies soon to the mix
Congrats by the way!!!