Since this seems to be the topic of conversation lately and since I know several people who will be having babies soon, I thought I would dedicate a post or 2 to car seats and child safety in the car. This is one of the 3 subjects that has become kind of a passion since having Gage (other 2 are breastfeeding and babywearing). There just seems to be so much outdated and misinformation out there on the subject, so I will do my best to give you a crash course :). My info comes from various places (www.cpsafety.org, www.kyledavidmiller.org, www.car-safety.com, as well as other message boards with cpstech members). We are also in the market for a convertible seat, so this has been on my mind a lot lately.
Expiration- Car seats expire after 6 years from the date of manufacture, at most (exception is the Sunshine Kids Radian-8 years). Some older seats have an "expiration date" that may be 10-12 years from the DOM and are incorrect. Newer research has found that the plastic in a seat breaks down over time, and the longest one can "live" before it is no longer considered safe is 6 years. If you have an expired seat, the best thing to do is to cut the straps, and write "do not use" in big letters with permanent marker before chunking it. Some fire stations and safety techs will take old seats for demo purposes, so if you can't stand to throw it away, see if you can donate it, but please don't give it to someone else to use or try to sell it.
Used Seats- Don't buy a used seat unless you know it's history. A car seat that has been in an accident, even a small one, can have tiny cracks in it that would cause it to fail for you. If you are in an accident with your car seat installed, your insurance company will buy you a new seat.
After-market additions to a seat are a no-no if they come between the child and any part of the car-seat. A head support that goes behind baby's head, something that connects to the straps, or an after-market cover are all against the rules. The reason is that they have not been crash-tested with those products so your child essentially becomes a crash-test dummy. Extra things that are soft could compress in a crash. Strap additions could cause the chest clip to be placed in the wrong location or prevent proper tightening. A rolled receiving blanket around baby's head or something that comes in the box with your seat are fine. Any additions can void the warranty and release the manufacturer from any liability should something go wrong.
Straps- Straps on any car seat should be untwisted and tight against the child. You should be able to work 2 fingers between the straps and your child at the collar bone, but not pinch a fold in it at the same location. The chest clip should be even with the arm pits, not down on the tummy. When Gage first got here, I didn't realize that I could tighten and loosen the straps every time we got in or out of the car. DUH! I was trying to cram his little arms through the straps without loosening them. It's SO much easier to do and you get a much better fit if you just let them out all the way and tighten each time you get in the car. I like to get him all buckled, tighten, pull on the chest clip to make sure I got all of the slack out of the part by his hips (those get turned and in the wrong place easily), then tighten again.
Installation- The middle is the safest seating position for a baby in a car seat. If you have more the one child in a seat, the least protected child should be in the most protected position (the middle). So, say you have a 3 month old in an infant seat and a 4 year old in a forward facing seat. The 4 year old should be in the middle and the infant outboard.
Seats can be installed with either LATCH or with the seat belt. Neither is any safer than the other in a correct install. LATCH is only safer because it is easier to get a good install for some cars and some parents. Be sure to check your vehicle's owner's manual for weight limits on the LATCH system...for many it is 40lbs, and after that you must use the seat belt to install the seat. No matter what the method, a seat should move no more than one inch at the belt path in any direction. Movement at the top of the seat (away from the belt) has no bearing on how well the seat is installed.
Added from Andrea's comment: You can go to any Major City Police Station and they will let you know if they have any officers trained in installation. They will assess your installation for free. After we installed our seat, I went by and they dispatched the officer to the station. Literally, he stood on Addie's base, in a squatting position to make sure it was as tight as possible in my backseat it was crazy. They train for a full week to have that certification and they provide it for FREE!!!
You can also go to http://www.safekids.org/certification/ and click on "Find a Technician." When I did it for my area, mostly sheriff's offices came up, but also, our local hospital and a church. The stats say that up to 90% of seats are installed incorrectly, so it really is worth it to get it checked!
Anyone in a car is safest rear-facing. To date, though, nobody has made a seat for anyone over 35lbs to ride that way. The old "rule" and most laws state that a baby should stay rear-facing until 1 year AND 20lbs. A child really should stay rear facing as long as they are within the weight limits of the seat, which in the U.S. is between 30 and 35lbs, depending on the seat. The reason is because in a crash, the forward forces throw the baby's head forward if they are facing forward, causing internal decapitation (breaking baby's neck). If rear-facing, the child is able to "ride it out" against the back of the seat, with his whole body, neck, and head cradled against the seat. Here is "the" YouTube video of crash tests forward and rear-facing.
As you can see from the video, legs touching the seat back is NOT a problem. There have been no reports of children breaking legs or hips because they were RFing, and even if there were, that's better than a broken neck.
Fit- There are height and weight limits for every seat. Be sure your child is not too big (or small) for the seat that they ride in. The owners manual will let you know the weight restriction, but height is not a set-in-stone kind of thing. A child has outgrown a rear-facing seat by height when he has less than an inch of shell above his head.
ETA: I edited to put this part in the "rear-facing" section instead of the "general" section, then forgot to paste it back in! Thanks, Jana for the comment that reminded me!
The straps for a rear-facing child should be in the slot at or BELOW their shoulders. You can move them up when their shoulders are level with the next slot.
Infant seats should be reclined to about 45 degrees. As the child gets older, the recline can be reduced but should never be more than 45 degrees.
Next Up: Forward facing and booster seats.