It's being used as a verb.
Cue the actor- he's missed his prompt.

Cue the musician- he was supposed to start playing.

Cue the lost girl wandering through the woods. Start the action.

In each case, this denotes a character getting a prompt for some sort of action. Used in the example you give, it would denote that the main character is being prompted to action, as in a play- cue the young boy walking across the street, for example. Meaning, at that moment the audience notices the young boy crossing the street.

It's being properly used. It's a narrative device.
( The Resident Loon Not a demographic. Do not measure., Tue 3 Feb 2009, 23:47, Reply)