Sue for lying

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My son was accused of "sexual touching" a 13y/o, he is 15. Eveyone knows (including the parents) that this girl is very permiscuis. Her own parents know she lies, but they are trying to get my son in trouble. We have witnesses including her own brother that know that this accusation is false. After all is said and done in a court of law and my son is proven innocent, can we sue them for defamation of character, embarrasement for my son and ourselves or something similar? We would like our expenses paid, and want this girl and parents to know that she cannot do this and get away with it.
Thank you,
Rocky