Issued a Citation After a Minor Said He Was Drinking at My Residence

My question involves criminal law for the state of: Wisconsin

The police came to my residence to investigate an assault on a minor by an adult. The assault allegedly happened in my yard. I had/have no knowledge of it and the only thing the officers knew of it was from the assaulted minor. After they knocked on the door I went outside to talk to them. I never let them in and could provide them with very little information. I also told them no one inside could help them either and ended the conversation and went back inside my house. (reason why they got upset and issued me an obstructing an officer citation, but thats for another post) That was the only confrontation with the cops at the party. They also issued me a ALLOW UNDERAGE ON LICENSED PREMISES 125.07 (3) citation. All of which was sent through the mail. After I got the police report it states that the minor's friend was taken for a police ride and identified my house as being the house that they were drinking at earlier in the evening.

Now I know Im not a Licensed Premises, but i know they can easily change that to what they meant.

I had strict rules against underage drinking at my party. No one was allowed to drink out of anything besides a clear cup that I provided after seeing their ID's.

My question is it really justifiable enough for a minor to simply "say" he was drinking at my house to the police?
I was under the impression the police would actually have to witness and/or card people they saw at or leaving someones household.

I plan to plead not guilty and would like to know if further evidence on my part would be helpful, i.e. signed statements from people at the party, pictures of my no underage drinking signs, ect.

The minor who says he was served alcohol at your party is a witness, and yes, that's enough to support a charge. Even if you're exceedingly careful about serving alcohol at your parties, it's usually pretty easy for a minor to get a drink.

If said witness doesn't show up to court how much legality does the officers police report hold? Sounds like it could be deemed hearsay. I guess the officer could be the witness to the minor identifying my house. This is all ridiculous because I know these kids were having their own party in the neighborhood. I only had like 12 people over at my house and I knew them all.

If the witness doesn't show up and you made no self-incriminating statements, it is unlikely that they could prevail at trial.