@Rocket98 In your conversation options is there an option to "Ask to Join Household? for the toddler?
Is the mother still appearing? Because I've asked a ghost Sim to join my household before and that has worked for me. So, my Sim's bff died in the jungle and I couldn't find her ghost. But she turned up at the Spice Festival and my Sim was able to speak to her and move her into the household. That was so I could revive her with Ambrosia and make her human again. But, if you don't get the "Ask to Join Household" option for the toddler then try it on the ghost. It will then show you the household and the toddler will be there, you can then move both of them across to the current household or just rescue the poor toddler.
I take it they didn't live in a lot anywhere to make it easier to find them? Apologies if that's a daft question lol. But you can possibly use your relationship list to invite the ghost parent over to the house. I've been able to do that before, actually quite recently when I killed off my Sim's fiance in a blizzard on Mt Komorebi. He was still on my Sim's list of contacts and I could invite him over and the option to add him to my household was there but I didn't use it.
Before you do anything I would quickly make a backup save so you have one save with the toddler still present, while you try to figure out how to rescue her.
I looked for a Cheat to try (if you use them) to find a lost Sim:
"Press Ctrl + Shift + C keys at the same time to open the cheat bar. On console hold down all four triggers at the same time. A thin textbox will appear at the top of the screen. Enter "testingcheats true" in the textbox to enable cheats.Write: resetSim (name of your Sim) (surname) For example, if your Sim's name is Bella Goth, you would write: resetSim Bella Goth."
Now I haven't tried this cheat myself I should say as I'm on Xbox Series X and certain cheats disable our achievements. But it's there for you if you wanted to try it. If you search for it that's what comes up.
Oh and yikers that's a bonny colour horse! If that happens again I'd file a bug report for that! The only time I've had an animal do that was because of a bug with the Mac makeup. It was glitching the appearance of other household members and in her case the only other one was the dog. He looked like that but glowing and shiny.
Edit: here's a few images of where I'd look when merging households, I don't know which you tried but the first is Manage Households filters and the second and third are in Household Split and Merge. I don't have any ghost households unfortunately I just deleted random ones in my weekly cull of extra Sims and the one dead Sim that I had has now gone on to rest in peace. In Household Split and Merge>Not in World all households are alphabetical.
Ok, it has taken me a while to find a save with my mom ghost still in it. She faded away a few saves back. And I had no way of contacting her. I thought I could call her but aparently she hasn't paid her phone bill being dead and all. So I guess I would have to play that household till she invited me out. That isn't too fun. But I see no other option. I wish I knew how she died and where! She was a townie. Ok next experiment!
@Rocket98You could see if she pops up if you select Travel, your list of friends and acquaintances will pop up and she might be on there. When my Sims have ghost friends they are available to travel with. If she is, you will get to see her in person and see what options are there and if you can ask her to join the household if the relationship is high enough.
You might find this useful if you haven't seen it, it also explains about ghost parents and Sims social services:
https://simscommunity.info/2022/05/11/guide-to-ghosts-in-the-sims-4/
If she was a townie that died, I take it you must have Neighbourhood Stories enabled which allows for life and death events for unplayed and played Sims. I play with it off in my Game Options to avoid changing my previous households.
