Check out these collections of auction pieces for young actors for inspiration:
The Methuen Drama Book of Monologues for Young Actors ed. Anne Harvey (2007) Methuen
TheMethuen Book of Duologues for Young Actors ed. Anne Harvey (1995) Methuen
Monologues for Young Actors ed. Lorraine Cohen (1994) Avon Books
Audition speeches for 6-16 year olds ed. Jean Marlow (2008) Methuen
And check out the National Theatre Connections. Plays commissioned annually for young people.