By Graham FisherCar seats are one of the most important pieces of baby gear you will buy, and keeping your child safe in the car means using the seat exactly as the manufacturer designed it. The American Academy of Pediatrics (AAP) warns that many aftermarket accessories, from cozy inserts to winter coat hacks, can interfere with how a car seat protects a child in a crash. Understanding what to avoid and what to do instead helps you make safer choices every time you buckle up.
Why aftermarket car seat accessories can be unsafe
The AAP’s guidance is clear: if an item did not come with the car seat, it has not been through crash trials with that seat and may interfere with the protection provided in a crash. According to the AAP’s car seat information for families, you should not use extra products unless they came with the seat or are specifically approved by the seat manufacturer. These products are not covered by any federal safety standards, and the AAP does not recommend they be used.
Many parents are surprised to learn that even items sold on store shelves or online can be unsafe. The AAP’s winter car seat safety tips note that just because a product is available at retail does not mean it is safe for use in a car seat. Always check that any accessory has been approved by the Consumer Product Safety Commission, and remember that the safest approach is to stick with what the seat manufacturer provides.
The winter coat problem
Bulky clothing, including winter coats and snowsuits, is one of the most common hazards parents encounter. In a crash, the fluffy padding in a coat immediately flattens out from the force, leaving extra space under the harness. The AAP explains that a child can then slip through the straps and be thrown from the seat. This risk exists for all ages, and the AAP even points out that wearing a puffy coat yourself with a seat belt is not a best practice because it adds space between your body and the belt.
To keep a child warm without compromising harness fit, the AAP recommends dressing your baby in thin, close-fitting layers. Start with tights, leggings, or a long-sleeved bodysuit, then add pants and a warmer top like a sweater or thermal-knit shirt. A thin fleece jacket can go over that. In very cold weather, long underwear is also a warm and safe layering option. The AAP’s winter tips also mention a general rule of thumb: infants should wear one more layer than adults, but you must remove any coat or blanket inside the car before putting your child in the car seat.
What the AAP says about harness fit
Proper harness fit is essential whether you are using a rear-facing or forward-facing seat. The AAP’s car seat information page describes how to check the harness: you should not be able to pinch any slack between your fingers when checking the harness straps over the child’s shoulders. The chest clip must be placed at the center of the chest, even with the child’s armpits. For rear-facing seats, the harness straps should be in slots that are at or below the child’s shoulders. When you switch to forward-facing, move the harness shoulder straps to the slots or position that is at or just above the child’s shoulders.
Multiple layers of clothing can make it difficult to tighten the harness enough, even if the child looks snugly bundled. The AAP advises that if you can pinch the straps, the harness needs to be tightened to fit snugly against the child’s chest. Getting the fit right is a key part of car seat safety, and it is one reason why thin layers are so important.
Safer ways to keep your child warm
Instead of bulky coats, the AAP suggests several alternatives that keep a child warm without placing anything thick between the body and the harness. You can add a blanket over the top of the harness straps after the child is buckled, or put the child’s winter coat on backwards over the buckled harness. Some parents prefer poncho-style coats or jackets that zip down the sides so the back can flip forward over the harness. The top layer should be removable so the baby does not get too hot after the car warms up.
For infants in a carrier-style seat, storing the carrier portion inside the house when not in use helps keep the seat at room temperature and reduces the loss of the child’s body heat in the car. Hats, mittens, and socks or booties also help keep kids warm without interfering with the straps. If your child is a thumb sucker, the AAP notes that half-gloves with open fingers can be useful, and keeping an extra pair of mittens handy is wise because wet mittens can make a child colder.
Car seat covers can be used, but only if they do not have a layer under the baby. Nothing bulky should ever go underneath the child’s body or between the body and the harness straps. The AAP stresses that you must leave the baby’s face uncovered to avoid trapped air and suffocation. Many retailers sell bundling products that are not safe for car seat use, so it is important to check that any cover goes over the top only and does not add padding behind the child.
Other accessories to avoid
Beyond winter gear, the AAP warns against a range of aftermarket products. Its winter safety tips say never to use sleeping bag inserts or other stroller accessories in the car seat. Similarly, the AAP’s general car seat guidance addresses products that claim to improve seat belt fit for older children. These unapproved devices may cause the lap belt to ride too high on the stomach or make the shoulder belt too loose, and they can even damage the seat belt. The AAP states that as long as children are riding in the correct restraint for their size, they should not need additional devices.
When shopping for a car seat, it helps to understand the different types available. Our guide to infant vs convertible vs all-in-one car seats explains the options and when each is appropriate. If you are considering a used seat, be sure to read our article on buying secondhand baby gear to know what safety checks to make. And once your child outgrows the harness, you will need to move to a booster seat that positions the vehicle belt correctly.
Accessory concerns at a glance
| Product or habit | Concern | Safer option |
|---|---|---|
| Bulky winter coat or snowsuit worn under harness | Padding compresses in a crash, leaving slack in the harness; child can slip out. | Dress in thin layers, then place a blanket or coat over the harness after buckling. |
| Aftermarket inserts (head supports, body cushions) not sold with the seat | Not crash-checked with the seat; may interfere with the protection provided in a crash (AAP). | Use only the inserts that came with the seat or are approved by the manufacturer. |
| Sleeping bag inserts or stroller accessories used in a car seat | The AAP says never to use them in a car seat. | Use a car seat cover that goes over the top only, with no layer under the baby. |
| Seat belt adjusters or positioning devices for older children | Unapproved; may cause lap belt to ride too high or shoulder belt too loose; can damage the belt. | Use the correct restraint for the child’s size; no additional devices are needed. |
| Car seat covers with a layer under the baby | Bulky layer can interfere with harness snugness and may pose a suffocation risk if the face is covered. | Choose a cover that goes over the harness only, and keep the baby’s face uncovered. |
| Any other add-on not sold with the seat | Not covered by any federal safety standards; the AAP does not recommend it. | Use only products that came with the seat or that the seat manufacturer specifically approves. |
For more on keeping your child’s seat in safe working order, see our article on car seat expiration and recalls. And if you are still choosing a seat, our Car Seats category page can help you compare features and find the right fit for your family.
Frequently asked questions
Can I use a head support that did not come with the car seat?
The AAP advises against using any extra products unless they came with the seat or are specifically approved by the seat manufacturer. The AAP notes that an item that did not come with the car seat has not been through crash trials with it and may interfere with the protection the seat provides in a crash.
Is it safe to use a car seat cover in winter?
Yes, but only if the cover does not have a layer that goes under the baby. The AAP’s winter car seat safety tips state that nothing bulky should go underneath the child’s body or between the body and the harness straps. A cover that fits over the top of the seat and leaves the baby’s face uncovered is a safer choice. Always make sure the product has been approved by the Consumer Product Safety Commission.
What about seat belt adjusters for older kids?
The AAP does not recommend these products. They are unapproved and may cause the lap belt to ride too high on the stomach or make the shoulder belt too loose, and they can even damage the seat belt. Children who are riding in the correct restraint for their size should not need additional devices to make the seat belt fit.
For more guidance on choosing and using car seats safely, visit our Car Seats category page.
Sources
- Winter Car Seat Safety Tips (HealthyChildren.org, AAP)
- Car Seats: Information for Families (HealthyChildren.org, AAP)
About Graham Fisher
Graham Fisher is part of our editorial team and reviews and edits our baby gear guides, checking product details against manufacturer specifications and owner feedback.
