The boy is the messenger in Godot. There are two identical boys in the two acts. They come to announce the fact that Godot will not arrive. The two boys constitute yet another confusion in the form of the operation of the double, which is a general pattern of the play.
The two boys are important in the sense that they expound Beckett's un-knowing subjectivity quite perfectly. Their patent answer is 'I do not know'. Beckett exploits a horrific as well as comic flatness and mechanical quality through their speech.
They also stand for an enigmatic innocence, especially when Vladimir loses his cool and abuses them. As Vladimir's words clarify, they also offer a subjectifying gaze for the two tramps to establish their existence.
The two brothers are like Cain and Abel and their dialogues about Godot's abode and his supposed treatment of them as well as their respective professions under him--all point to a seductive Christian symbolism, built into the play.
well, thats a good question, see the boy could represent in terms of looking at the characters Gogo and Didi/Estragon and vladimir the boy could represent growth in time or the progression in time as both Estragon and Vladimir are old and wasted waiting for death. The boy is a sign of living and hope even if how hopeless it may seem to be for them both. That even though throughout the play nothing happens, no one comes (Godot) never comes, whose to say the boy , Pozzo or Lucky isn't Godot. Just hope this opens up more avenues for you when looking at this question.