NEW ORLEANS — A new set of laws takes effect in just a few days regulating how long your children have to be in car seats.

Every child will be affected by the new rules. 

A few changes that stand out:

  • Children, ages 4 through 9, will need to be in a booster seat, unless they meet certain height and weight requirements.
  • And at 9-years-old, they can sit without a booster seat, under one condition, the belt must go across the hips and the strap across the chest.

That might not sound like a big deal, until you hear about one little girl who suffered horrific injuries in a crash, not from the impact, but from not being properly strapped in. 

RELATED: New changes coming to Louisiana's child car seat laws

Molly Thornhill's mom, Melanie, never thought her little girl would be able to play, run or dance again. It was just October when she got a phone call from Molly's dad with devastating news. 

"I answer the phone and I hear his panicked voice and he says, 'Get to Winnfield Hospital now. Me and Molly have been in a car wreck,'" remembers Melanie Thornhill, of West Monroe. 

Someone who was speeding, crossed the center line on a highway near their home in West Monroe and hit them head on. It's still emotional for a mother remembering it all.

"When they were loading her in the helicopter to airlift her out of there, she was calling for me, and I couldn't go with her. And I still hear that a lot," Melanie said. 

Molly had multiple surgeries on her severed intestines in Lafayette, but then was brought to Tulane Lakeside Hospital in Metairie for the devastating back injury. 

Tulane spine deformity surgeon Dr. James Bennett said Molly had what's called a "chance fracture." Not only are the ligaments and muscle ripped apart, but the vertebral body, a bone in her spine, is split in half. 

It happened because even though Molly was locked in her seatbelt and shoulder strap, she put the strap behind her.

"It like rubs on your neck because I was too short, so I went like ugh, and put it behind me," said Molly Thornhill, 10. 

"This is why seatbelts back in the 60s were changed to over the shoulder harnesses, because this was a common injury pattern and that's why they put shoulder harnesses on to them," Dr. Bennett explained.

Dr. Bennett put rods and screws in Molly's back so the ripped bone can fuse together. She will have a normal life, but he has seen two injuries like this recently. 

"It turns out, a lot of my nurses do that with their grand children and they don't think anything of it," Dr. Bennett said.

This is why a booster seat, used so the shoulder strap can hit in the right place across the chest, is imperative. 

"We never really thought about the importance of that until this happened," Melanie said. 

When Molly is asked if she will ever put the strap behind her again, she shakes her head no and says "Ah ah." 

And that is the message they hope will prevent another child from having a scare like Molly did.

Editor's note: The father, who was driving the car at the time, believes his daughter put the shoulder strap under her arm, rather than behind her back as she remembers it. Either way, it was just as dangerous. Experts say that the shoulder strap should be across your chest.