Pointing a finger and going "bang" does not warrant suspension. If it's against school conduct (which it shouldn't be if this took place on the playground), it warrant's a respectful warning to the child who probably didn't know any better. If the child keeps doing it in defiance, then a conversation with the child's parents is in order.
A 1st grader pointing a finger and going "POW" is in no way violent. Punching a teacher or hitting another child for spite or in anger is violence.
I don't remember my parents sitting me down at 6 years of age and reviewing a manual of rules and regulations with me. Maybe we should have children attend law school first, before sending them to pre-school, so they will understand all of the asinine rules and regulations passed by school board attorneys!