It’s a milestone many little kids look forward to: Moving out of their car seat and into a big kid booster seat. Booster seats are meant to position adult seat belts properly on kids who have outgrown car seats, but one mom is urging parents not to rush into using them before children have maxed out the weight limits on their five-point harness car seats.

Mom of four Sarah Sutton was recently running errands with her kids— 6-year-old Alayna, 5-year-old Liam, 3-year-old Ryder and baby Aynsley, age 2—when she says another driver ran a red light and crashed into the family’s SUV head-on.

“Alayna and Liam were wanting to move to boosters as ‘car seats are for babies,'” Sutton tells Motherly, noting that all of her kids were strapped into a Safety First Air 65 car seat when they were hit. “I am so glad I kept them in a five-point harness and will continue to do so for as long as I can.”

 

In a Facebook post that has gone viral, Sutton urges other parents to keep their children in car seats for as long as possible, even if they’re begging to move up to a booster. While all of Sutton’s children suffered concussions and the three oldest sustained some injuries where the car seat belts cut into their skin slightly, the harnesses prevented much worse injuries as they kept the kids from being thrown in a crash that Sutton fears would have been worse if she wasn’t driving her heavy Chevy Suburban.

“The only car we will ever feel safe in is the Chevy Suburban,” says Sutton, who has already replaced her vehicle and her car seats. “They are now in the updated version Grow and Go EX Air from Safety First.”

The kids kids have plenty of time left in those seats before Sutton converts them into booster mode. The Grow and Go EX Air from Safety First is built for kids up to 65 pounds when used as a forward-facing car seat (smaller babies can rear-face) and can be used as a be belt-positioning booster for kids weighing 40 to 100 pounds.

As Sutton points out in her now viral post, “there are many [other] car seats on the market that allow us to keep them in a five point harness past the age of four.”

Related: A parent’s guide to car seat safety: Tips, rules & product picks

In fact, a kid might be eight years old before they max out of their convertible car seat, as many of those seats are built to hold kids who weigh up to 65 pounds. According to the American Pediatric Association (APA), parents should keep kids in car seats for as long as possible, until the child has outgrown weight or height limits.

After that, it’s finally time to put your kiddo into a booster (or in Sutton’s case, convert your convertible car seat into a booster.) The weight limits on many boosters can go up to or even beyond 100 pounds, and kids are typically in those from about 8 to 12 years old (or until they are about 4 feet, nine inches tall), according to the APA. Boosters aren’t something parents should rush into, but they are a step we shouldn’t skip.

 

“Without a booster, a child in a crash is more likely to have abdominal and internal organ injuries since adult belts don’t fit correctly,” Joseph Colella, Director of Child Passenger Safety for the Juvenile Products Manufacturers Association, previously told Motherly. “A booster positions vehicle seat belts on the strongest parts of the body and away from the vulnerable abdomen.”

Booster seats are great, but Sutton’s story proves that they really are for the biggest big kids, and that—contrary to what Alayna and Liam once thought—convertible car seats are not just for babies.

A version of this story was published May 9, 2018. It has been updated.