I'm going to lock this as I'm not even sure if it was still an issue after the infant patch.
If you do still have issues with toddlers, please create a new thread.
I can also confirm seeing this is one save recently. There was a similar issue a long time ago that was fixed and at that time it was tied to the parent having the beloved trait (which is earned by completing the friend of the world aspiration). In my save the parents both have that trait, as does the other young adult living there and they all have to introduce themselves, however the sibling of the toddler does not and nor does another sim, who is a teen who does not have the beloved trait. Do any of your sims have the beloved reward trait?
Best regards,
Jennifer
Now that you mention it, I didn't have this problem before completing the Friend of the World aspiration. I'm playing a 100 baby challenge and I didn't have a problem for the first 50 babies, which was around the time I completed that aspiration.
