What does Charles Dickens mean when he says that every child in the last house Scrooge and the spirit visted was "conducting itself like forty"?

Dickens is referring to the fact that the children were extremely active and noisy, and the scene was chaotic.

The noise in this room was perfectly tumultuous, for there were more children there, than Scrooge in his agitated state of mind could count; and, unlike the celebrated herd in the poem, they were not forty children conducting themselves like one, but every child was conducting itself like forty.

What old poem is Dickens referring to?