Should You Move Your Toddler to a Booster Seat?

Many parents wonder if their tall young child is ready for a booster seat, or if there's an age requirement. It's easy enough to check the weight and height limits of various boosters to see if your little one will fit according to manufacturer instructions. But many parents don’t realize that there is also a maturity requirement to ride in a booster.

First, know the difference between car seats and boosters:

  • A car seat is any seat where the child uses a five-point harness as their restraint.
  • A booster is any seat the child sits on and wears the vehicle’s seat belt across them as their restraint.
Moving a toddler to a booster seat
Verywell / Brianna Gilmartin

Booster Seat Age

If you can safely keep your child in a harnessed car seat for a while longer, do it. The American Academy of Pediatrics recommends that kids use a car seat until they reach the maximum height or weight for that five-point harness. This is usually not until age 5. Three-year-olds are not ready to ride in a booster seat, even if they fit within the manufacturer's height and weight guidelines.

To sit in a booster seat, your child should:

  • Be mature enough to sit properly in the booster for the entire trip (no slouching, no leaning over, no messing with the seat belt)
  • Ideally, be at least age 5 (even though many boosters start at age 4)
  • Weigh at least 40 pounds (even though there are a few boosters that start at 30 pounds)
  • Have exceeded the height or weight limits on their harnessed car seat

Many convertible and harness-to-booster car seats have harnesses rated to hold kids up to 65 pounds. In fact, children in the U.S. today can often stay in a harnessed car seat until age 6 or beyond. Thanks to advances in car seat safety technologies, 4-year-olds that might have been moved into a booster 10 years ago can still safely ride in a rear-facing car seat. Even fairly tall children can remain rear-facing through toddler years and then switch to a forward-facing harness until kindergarten age. For most kids, even those in the 95th percentile for weight or height, there shouldn’t be a reason to move to a booster before age 5.

Should You Wait to Switch?

Any step up in car seats — from rear-facing to forward-facing, from the harness to booster — is actually a step down in safety. The 5-point harness spreads crash forces over more points on a child's body, lessening the potential force any one part of the body must take in a crash. If your child's harnessed car seat is used with a top tether, he or she can benefit from a reduction in head excursion during a crash, which translates to fewer and less severe head and neck injuries.​

Many booster seats wouldn't be appropriate for a smaller child because of the minimum height and weight. While some high-back booster seats have a minimum weight of 30 pounds, there are lots of other booster seats that require a child to weigh at least 40 pounds before use.

From a practical standpoint, parents find that it is easier to keep the child sitting properly when in a car seat than in a booster; in a booster the child can unbuckle themselves more easily than in a car seat.

The seatbelt cannot protect a child who is not in the proper position. Most children cannot be trusted to sit properly until at least 4 years old.

Many parents find that their child is actually much older than 4 before they can be expected to sit still in a booster.

If your vehicle has lap-only seatbelts in the rear seats, keep your child in a harnessed car seat as long as possible. Harnessed seats can be installed with a lap-only belt. Booster seats absolutely must be used with a lap/shoulder belt. Extended harnessing, or using a harnessed car seat with a higher weight limit, is vastly preferable to moving a child into a lap-only seatbelt.​

How to Determine Car Seat Fit

If you think your child is outgrowing his or her harnessed car seat, first be sure that you're checking the right signs to judge the fit. Pay close attention to the weight limits of the car seat and be sure you're looking at the forward-facing harness weight limit, not the booster weight limit (if it is a harness-to-booster seat).

Also, check the manufacturer's instructions for other ways to determine that the seat is outgrown. When your child is forward-facing, the harness slots should be at or above the child's shoulders. When the shoulders are above the top slots, it's time to change seats. A forward-facing car seat is also outgrown by height when the tops of the child's ears reach the top of the car seat shell unless the manufacturer states otherwise in the instructions. Most children outgrow harnessed car seats by height long before they outgrow by weight, particularly with the 65-pound seats.

If your child truly has outgrown a 40-pound limit harnessed car seat and is still under age 5 or not mature enough to sit properly in a booster for the entire ride, it's best to look for a car seat with a higher harnessed weight and height limit.

There are many harness-to-booster car seats available today with a higher harness limit that later become booster seats if you're concerned about buying another car seat and then a booster. As long as it is used properly, any car seat with a higher harnessed weight limit would be a good choice. The range of car seats available today means no family should struggle to find even a budget model that allows their child to remain safely harnessed to a minimum of age 4, and most likely far beyond that.

Still not sure if your toddler is riding safely in the car? Visit a nationally certified child passenger safety technician (find one via SafeKids or the National Highway Traffic Safety Administration) to check the installation and usage of your child’s car seat.

Heather Corley is a certified Child Passenger Safety Technician-Instructor.

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