[Jamestown1630]

The parent may not have wanted the child’s sex reported, or just stayed away from reporters altogether.

Again, this is not improper usage; it’s been around for hundreds of years, long before anyone started playing around with ‘gender’ in language:

https://en.wikipedia.org/wiki/Singular_they

[Blennos]

Maybe the child was royalty. They get the benefit of plurality due to their high noble status.

[Petrosius]

The parent may not have wanted the child’s sex reported, or just stayed away from reporters altogether.

Then the reported should have just said "the child."

The article you referenced shows that the singular "they" was considered incorrect until recently, i.e. until pushed by members of the "gender neutral" LGBT crowd. If they can advocate for its use, those who do not accept their ideology can advocate for its incorrectness.