From the Capital Times:
Starting January 1st, Wisconsin authorities will start enforcing a law that requires children who are at least 4 years old but younger than 8 to travel in a booster seat while in the car, unless they are 4 feet 9 inches or taller or weigh 80 pounds or more. Wisconsin law already required children under 4 years old to be in a safety seat.
If a child 4 or older, but not yet 8, is unrestrained or not properly restrained, drivers will face a $135.60 fine for a first offense and $184.50 for a second offense. For children younger than 4, the fine is $160.80 for a first offense.