My question involves criminal law for the state of: Kansas

Hello....I am a new guy. I did a few searches and was unable to find an answer to my question. It has to do with a city ordinance. Not sure if it is criminal or an infraction though.
Now I am not completely ingnorant of the law, but I am far from an expert.

This is my situation. My step son was issued a ticket for a curfew violation. However, this violation was not witnessed by a police officer. It was witnessed by a citizen, ( a citizen that hates my wife by the way.) My step son was staying at a friends house. He was with 3 other teens, and 2 adult parents. It simply wasnt him that this person saw, thats if she even actually saw someone.

My question, doesnt a cop have to witness an infraction to issue a ticket? And even if he doesnt, doesnt he have to investigate both sides before issuing a ticket?

This is going through municipal court in a very small town. I dont want to get a $300 lawyer to fight a $100 fine. But, its the principle of the deal. Trying to teach my son to stand up for yourself and not just roll over and take it when you have been wronged.
We went to court and pled not guilty, and a trial was set up. I know the prosecuting attorney fairly well, and plan on talking to him soon since I am representing myself in this deal. I would just like a little ammo before I go in. Mostly, is the ticket legal in the first place.

I thank you for your time and consideration.