There are other ways to handle it. Filing criminal charges against a six year old...? Especially one who’s autistic? The right way to handle it would be to separate the child from the class immediately, to make him sit in another room (detention), call the parents in immediately, and have a meeting between the principal and the parents. Demand the child be put into a different class/program.
Criminally charging the kid is just a technicality to CYA from the parents being able to sue. Parents nowadays can sue if the teacher looks crosseyed at the kid. The schoolboard has to protect itself. And what if the kid assaulted another student and the school knew the kid was a threat and did nothing? Another lawsuit?