You can't change how that woman is 'protecting' her daughter.
They don't like your son now... and for that reason.
He put his hands down her pants.
I have a daughter. If a boy did that to her, I would also explain to her to stay away from that boy. AND though, my daughter speaks up. She would have told your son, back off.
Sure at 6 years old, the kids were probably just goofing around.
Still. Now that other Mom does not like your son. Because of what he did.
Her daughter, is being a child and does not understand these things... in an adult manner or as a parent would. They don't understand why things like this are a big deal or not.
They are 6 years old.
Well so it happened a year ago.
That Mom is doing what she feels is best.
That is her right.
They don't know your family or that your son has sisters and that he went to counseling.
She is being, a Mom. A Mama Bear.
They don't have to like your son.
And now the Mom has a reason to stay away from your son and her daughter too.
She is not 'punishing' your son.
She is protecting her daughter.
But eventually, in school a Parent has to realize they cannot control everything nor all kids.
But so on her end, she has to teach and guide and educate her daughter... on appropriate/inappropriate behavior, and how to handle it & social situations, and report it etc. She has a daughter.
Not all kids will be liked by other kids or parents.
Whether there is a reason or not.
And a child has to learn... that what they do... IMPACTS others, and other peoples impression... of them. Now and later.