Are you sure your son is scheduled for an arraignment? Of course not getting arraigned is the best way to go, but, it is often very difficult to do so.
You don't need to explain this approach to a lawyer, any lawyer you hire should have an idea of where to go with this case.
If you dont' want your son arraigned you need to hire a lawyer BEFORE arraignment.
THESE are very serious charges and if convicted your son could end up having to register as a sex offender. You need a lawyer.
Get a criminal defense attorney right away. Do it immediately.
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Not being arraigned would be ideal, but that may be outside your control. This charge is a felony, so you do not have the right to a clerk's hearing before the complaint issues. If the arraignment is already scheduled, then the delinquency complaint has issued and not having the arraignment is very unlikely. One possible way to avoid the arraignment is to convince the prosecutor to dismiss the charges pre-arraignment, but given the nature of the allegations, this is not very likely to happen.
A tactic the police may try is to have your son come in and "give his side of the story". Do not allow your son to speak to the police, not even if he denies any wrongdoing. His silence cannot be used against him, and in a he said/she said case that was not reported for two years, the police are likely to seek out a confession to bolster what sounds like a weak case.
You need to retain a lawyer who has experience in child sexual assault cases and juvenile delinquency defense. The proper pretrial investigation and discovery motions practice will be essential in putting together the best possible defense.
Best of luck,