The Secret of Azuron by J.R. Kearney
What if your boy was the only one who could stop the greatest evil the world has ever known? Eleven-year old Landau discovers a treasure that will have every creature of myth and legend in pursuit of him. With the aid of his company, an odd teaming of a wizard, knight, assassin, gladiator, barbarian, mercenary and amazon, Landau must bring his treasure to the Capital to convince the Imperials who they are currently at war with to side with them and unite before the real enemy destroys them all. But the enemy constantly follows, Landau's companions despise each other, and all he wants is to complete his quest so he can return home - but what chance does a kid have against the creator of all things evil?
The first book in 'The Sword Empire' series.