Birds sang above them and chattered like school children this sentence is an example of

Answer: A simile.

Explanation:

Smilies are exaggerative phrases used to describe things in greater details by comparing two unrelated (to a certain degree) things. They must use words such as "like" or "as" to show the connection is not literal. It is not a simile if there are no connection words, and instead the exaggerative nature is assumed and implied from the context clues. An example of a context clue could be the absurdity of a comparison.

Birds sang above them and chattered like school children is an example of a simile.