As I understand it, the Attorney for the Minor can file a motion to suppress, but it is soley up to the judge's discresion(sp). He will get a lot of shit from the DA's office if he does. You see, after you Mirandize a person (minor or not), they basically take responsibility for EVERYTHING they say afterwards. But under some circumstances (inebriation, mental stability, emotional stability, and sometimes phisical condition, like if he just got the crap beat out of him), the judge will throw out the confession because it is obvious that the Minor was not in his usual state of mind.
But without knowing the details it is difficult to give a more detailed explanation/approach for the defence of the minor.
By the way, your wife's friend is a moron if she believes that just because you haven't turned 18, you are too ill-equiped to take responsibility for your own actions.