In Wisconsin, a child can use a booster seat starting at age 4 and 40 pounds. State law requires children to remain in some form of child safety seat until they turn 8, making the booster seat the standard restraint for most kids between ages 4 and 8. Before age 4, children must ride in a forward-facing car seat with a harness.
What Wisconsin Law Requires
Wisconsin’s child passenger safety law, under Section 347.48 of the state statutes, breaks down into two stages. Children must ride in a forward-facing car seat with a harness until they are at least 4 years old and weigh at least 40 pounds. Once they hit both of those thresholds, they can transition to a booster seat, where they stay until age 8.
Both conditions must be met before moving to a booster. A 4-year-old who weighs 35 pounds still needs a harnessed car seat. Similarly, a 3-year-old who weighs 42 pounds legally needs to stay in the harness seat.
A first offense for not having a child between ages 4 and 8 properly restrained carries a total penalty of $150.10.
When a Child Can Stop Using a Booster
Wisconsin law allows children to use a regular seat belt at age 8, but age alone doesn’t mean the seat belt will fit correctly. Most safety organizations, including the National Highway Traffic Safety Administration, recommend keeping a child in a booster seat until the seat belt fits properly, which typically happens around 4 feet 9 inches tall. Many kids don’t reach that height until age 10 or 12.
A booster seat raises a child so the vehicle’s lap and shoulder belt sit in the right position. Without it, the shoulder belt often cuts across a child’s neck or face, and the lap belt rides up over the stomach instead of sitting low across the upper thighs. Both of these positions increase the risk of serious injury in a crash.
The 5-Step Seat Belt Fit Test
Before ditching the booster, you can check whether your child is truly ready for a seat belt alone. UW Health recommends a simple five-question test:
- Back position: Does your child sit all the way back against the vehicle seat?
- Knee bend: Do their knees bend comfortably at the edge of the seat?
- Shoulder belt: Does the belt cross the shoulder between the neck and arm, not across the neck or face?
- Lap belt: Does the lap belt sit low, touching the thighs rather than the stomach?
- Staying put: Can your child stay seated like this for the entire trip?
If the answer to any of those is no, your child still needs the booster. Kids who slouch, lean to the side, or tuck the shoulder belt behind their back lose the protection the belt is designed to provide.
Back Seat vs. Front Seat
Wisconsin law does not specify a minimum age for riding in the front seat, but the NHTSA recommends keeping children in the back seat through at least age 12. The back seat is consistently safer in frontal crashes, which are the most common type of serious collision. Front-seat airbags deploy with enough force to injure a small child, even one in a booster seat.
Getting Your Seat Checked
The Wisconsin Department of Transportation runs car seat inspection events around the state where certified technicians check that seats are installed correctly and sized appropriately for your child. You can find upcoming events through the DOT’s child safety page. These checks are free and take only a few minutes, and studies consistently show that a large percentage of car seats are installed incorrectly. Even if you’ve installed seats before, a quick check after switching to a booster is worth the stop.