Hire an attorney right away. An attorney may be able to use the probation violation as an "up front" punishment as a way to convince the DA at a precharghing conference not to charge a battery or to pursue other charging or diversionary options. Karyn and Michael are correct in thier answers: get an attorney now.
Karyn is correct. If you are facing any felony you really need an attorney! If you have one and you don't know what happens at a status confrence you need to talk to your attorney. If they can't or won't answer this question you may want to find a new attorney.
Very likely if it is in a jurisdiction that posts ordiance violataions on the Wisconsin Circuit Court access website. You may want to get an attorney from your area on this because, in certain circumstances if the Judge is willing, this could be puled off the website. However, I'm not sure what Milwaukee courts might do with this but I've had success with this upstate.
According to Wis. stats. sec. 939.12 "A crime is conduct which is prohibited by state law and punishable by fine or imprisonment or both. Conduct punishable only by forfieture is not a crime." An OWI 1st in Wisconsin is punishable only by forfieture as long as there was no accident or other possible attenuating circumstances.
Try looking yourself up on the Wisconsin Circuit Court Access (CCAP) website. Is it listed? If not you should be aware that a potential employer will not likely be aware of your underage ticket. Secondly, unless the ticket was punishable by a potential jail sentence it was not a crime. If you are not asked specificaly about prior crimes do not offer the information. If it's not a crime, if it's not on CCAP then don't share it with your potential employer unless they ask the specific qiuestion...