The lack of word suggests the opposite, that it was extremely common. Indeed, historically, nearly everyone would have lost a young child, and many people would have lost an older child.
Orphans and widows were also important legal categories. Children without a father needed a legal guardian until they turned 18. Married women (at least under British common law) were not separate legal entities from their husbands. So each category needed a defined term. Parents who had lost children were in many cases just "parents", since families were much larger and it was probably the rare large family who had not experienced the death of a young child.
The lack of words suggests the opposite of the opposite: because it was so common (at a societal level), it was so traumatic (at a societal level). So maybe the lack of word suggests it was so traumatic.
The fact that it was common doesn’t make it less traumatic.
Everything is relative and our expectations are set by society and what is common. Today, losing a child is pretty uncommon. 3-4 generations ago if was very common. You expected to have 4-10 children and to lose one or two. It wouldn't be a pleasant experience, but I think it's incorrect to say it wasn't less traumatic (you expected it, you lost a lower percentage, etc). To quote Clint Eastwood's character in Gran Torino, "You're geared for it".
You're missing the point - check out the parent of the comment you're replying to.