Defendants are allowed to defend themselves. In your case, since your son is only 14, I doubt that is an option.
If the facts are exactly as you state them, there is indeed a good chance the State will not proceed or offer diversion, but...if the facts differ in some legally significant way, or even factually because you may not have the whole story yourself, then your son faces a potential sex-offense conviction which can haunt him for the rest of his life. Is this ridiculous? Some would say so...when I was 14, I cannot imagine a similar fact pattern getting to court, let alone resulting in something as serious as a life long classification. But that was then....
So, before you barge ahead, with little or no understanding of your son's rights as a juvenile, in terms of speedy trial dates, available services, discovery, and the like, please consult with an attorney who has experience in the juvenile courts. If you cannot to hire one, make sure you assist the public defender in any way possible.
As a parent, you do have a major role to play - the court will look to you in some measure to determine how to handle the disposition of this case. Be available, have an open mind, and don't try to bully your side of the story before you know your options fully. Just the admission you placed in your question can seal the deal if the State does file the petition for this charge.
Speak with a qualified attorney before doing or saying anything, even if it is just the public defender. Make an appointment to see one as soon as they are appointed.
Typically juvenile "sex crimes" such as these (and by statute, both kids can be charged for the lewd conduct and lewd molestation) you are describing don't get picked up by the State. However, because your son is 14, if the State does, he is facing absolutely horrible long term consequences. You need to get your son an attorney pronto. And no, you can't do it yourself, unauthorized practice of law is a felony.