If you don't have it already, get the Pescado's Lot Debugger from MATY.
Any time you have a sim or object turn invisible, you can Force Error using the Lot Debugger to make invisibles visible again. It will reset the lot, making those as school or work pop in by the mailbox and possibly get dinged for not going to school or work, so use it when most are home. 6 am is best.
The safeguard for preventing infant and toddler death, and even children in the case of neglect, is the Social Worker. If the little one's needs reach a critical level, the Social Worker shows up and takes the child. If you have a mod that prevents the SW from appearing, death may occur.
I don't have a mod for that, but I think since no motive was critical but energy she didn't come.

Thanks very much for letting me know about the lot debugger. I'll go get it. (I'm sure my Sims and their kids thank you too, haha.)