"Prodigal" does not refer to someone who has gone away. It means wastefully or recklessly extravagant; giving or yielding profusely; lavish. Or, if used as a noun, means "a person who spends, or has spent, his or her money or substance with wasteful extravagance; spendthrift."
Okay? The famous "prodigal son" of the parable was a guy who went through his money as though it were water after leaving his family; the prodigality was in the spending, not the leaving.
So every time I hear of "prodigal sons returning", I grit my teeth (especially when it's applied to soldiers in Iraq — great way to honor our armed forces, by accusing them of leading dissolute lives over there!)