MADISON, Wis. (AP) – A federal appeals court says the parents of a 6-year-old Wisconsin boy charged with sexual assault can’t sue prosecutors and others.   The parents contended Grant County officials violated their civil rights and those of their son by overzealously investigating the case. They say their son was targeted because the girl’s father is a well-known local political figure.  Court documents say the boy was playing doctor with a 5-year-old girl and her twin brother in September 2010 when the girl’s mother thought the boy touched her daughter indecently. That led to juvenile charges of sexual assault that were later dismissed.  The parents’ lawsuit also was dismissed, and the 7th U.S. Circuit Court of Appeals upheld that decision Friday.  The court says investigators overreacted but “poor judgment does not violate the Constitution.”