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I do not practice in Pennsylvania and it sounds as if 12 year old's mother has already discussed her son's case with a local attorney. Here is what I wrote when responding to a similar question from Maryland a few minutes ago:
"You should follow that attorney's advice. The primary right your child has is the right to remain silent.
"By following that advice though and not letting your son talk to the police or child protective services (CPS), it may incline them toward concluding that your son (sexually?) touched the 3 year old because of something that happened to him. They may attempt to conclude that he has been abused or is at risk of abuse and try to coerce you into putting him in treatment. Unfortunately, anything he says in such situations can be reported to CPS. The only place that a person in your son's situation can speak in confidence is with a lawyer hired to represent him.
"It sounds as if your son needs a lawyer immediately."