Asta's son's name is Crispin. Crispin is the hero of the story and the companion of Bear. The title is written as it is, with a colon after "Crispin," to indicate a subtitle to the story.
The title may have been more clearly and correctly written "Crispin and the Cross of Lead." This is because a colon indicates a very close relationship between what comes in front of and what come after the colon, indicating that what follows is an expansion on what came before, not an addition to it. So technically, by the rules of puntuation, the colon does indicate that "Crispin" and "The Cross of Lead" refer to the same entity or concept, which is true metaphorically and symbolically but not actually.
Crispin is a name of Latin origin and means "curly-haired." In the third century, Saint Crispin became the patron saint of shoemakers. While this may seem a strange association for a name for a hero of a Medieval adventure drama, bear in mind that Bear (no pun intended) teaches Crispin about social and political structure in England as they walk the roads while covering many, many miles. So perhaps the humorously ironic association of our boy hero Crispin with Saint Crispin, guardian of shoemakers, makes sense after all.
Lead is a metal that is of little ornamental value of itself, very unlike gold, silver, or platinum. However lead was important in Medieval times because of its association with the art of alchemy and with astrology. First, in astrology, lead is the symbol of the planet Saturn, which represents duty, self-control, and relationships with fathers. This correlates with the themes of the story and with the source of Crispin's adventures and character development.
Second, in the ancient art of alchemy, the base metal lead is changed, or transmuted, by the properties of the Philosopher's Stone and fire into pure gold. So even though Crispin's lead cross has no name, it has a powerful symbolic importance in association with Crispin's journey in life as he is transformed from a fearful boy into a strong and independent, compassionate young man.
I this novel the son's name is Crispin. :)*.
In the novel "Crispin-The cross of lead" Asta's son is a name for the main character that he has had from the villagers of Stromford. His real given name from birth is Crispin after a revered saint of the time period. The Lead cross does not have a name.