Whenever a couple has any kids at all, there is always a youngest child and an oldest child. Sometimes, they are the same child.

There is not always a "middle child" because that requires at least 2 other children to exist.

You're trying to say that the "third child" is going extinct, which matches what the article is saying in a different way.

> Whenever a couple has any kids at all, there is always a youngest child and an oldest child. Sometimes, they are the same child.

Technically, that's an only child and that has articles all its own...

Right. A lot clearer if we use absolute cardinals here: the second child is now the youngest, whereas before they were the middle child.

There are both cultural/traditional and [epi]genetic implications of birth order, so this might imply a better or worse suitedness of the role of youngest-child given differing birth orders of the title-holder.

Well no... the middle child only comes into existence upon the introduction of the younger child.

can't tell if trolling or ingenious..