Infants and toddlers left uncared for while at work/school

Frankly, I hate playing with infants. Once you have more than one, the game starts glitching and bugging out. Nannies are useless because they tend to neglect the kids; my main couple hired a nanny for their first kid, and when they returned home from work, the poor girl was out on the sidewalk with dirty diapers and starving. They fired the nanny and then took turns staying at home caring for the kid while the other one went to work. Another one of their infants ended up in High School with his bigger sister. No idea how he got there. The twins kept glitching in and out of their cribs, nannies were standing around doing nothing and putting the kids on the floor... a total nightmare. It does get better with toddlers because they are a little more independent, but it's still very frustrating. The only solution I found is to make the parents take days off from work so they can take care of their kids or, in one case, do freelance work from home. I also try to get them to reach their infant milestones as quickly as possible so I can age them up to toddlers.

I don't tend to play with those life states, but I do recall in the past that this often happened when there is no highchair on the lot. Apparently the highchair was necessary. I have no idea if that is still the case to this day.

In note of starving infants and toddlers, though, if they end up with the messy eater trait, you may end up with the problem I had: No matter how often I fed her, she took so long to eat that when she was done her hunger bar was lower than it was when she began. My Sim could have fed her nonstop, but it wouldn't help because the kid splattered all of her food on the or stared around into space. Fun times.

That's why you have your parent sim hire a regular Nanny for the children. Not that she's 100% reliable, but when it comes to sims, 95% isn't bad. ;)

When first confronted with this problem, I did what was mentioned in an above response. I cheat up their needs, then I took it a step further, by preventing it to degrade. I'm sorry they didn't give us the same game mechanics as we had in Sims 3 wherein if you followed a Sim to work and saw a red bar on a family member left at home, we could pop on over to the household, fix the issue and then pop back to the working Sim. Not so easily done in Sims 4.