syntax - Is みんな being used as a "counter"?

This is from Minna no Nihongo Chapter 15. It's a description of Santa Claus.

でも世界の子供はみんな私を知っています。

みんな seems like a counter of sorts (I don't know how else to describe it) for　世界の子供. I always thought it was of the same grammatical category as 彼 and 彼女. So is みんな basically a "counter"? All the time? Most of the time? Depends on the situation?

Answer

I think 皆{みんな} can mean "all" when used adverbially, as well as "everyone" or "everything":

でも世界の子供はみんな私を知っています。
"But the children of the world all know me."

You can also use みんな to refer to more than people:

チーズは皆食べられてしまった
"All of the cheese has been eaten."

There's some more examples at the Yahoo dictionary definition for 皆{みな} (for information on the difference between 皆{みんな} and 皆{みな}, see also How do you know when to use みな or みんな?)