First, get a lawyer as your son may have a defense to the charge.
If he should plead or if the charges are found "true" ("true" is basically the juvenile court equivalent of "guilty") then he could face up to 90 days, which is the juvenile maximum for each misdemeanor count. However, because he has turned 18 before disposition ("disposition" is basically the juvenile equivalent of "sentencing"), the court will have the option of imposing all or part of that time in jail rather than DH.
Depending on your son's record he may be eligible for a diversion program. Even if he isn't, it is far from a certainty that the court will impose much if any jail. An attorney may be able to work something out to keep jail off the table.
Matthew C. Bangerter
38109 Euclid Avenue
Willoughby, OH 44094