The safest position for a child to travel in a car seat is rear-facing, that is, with the child facing backward in the car. The ideal would be to maintain this position for as long as possible, since in the event of a collision, the child's body is much better protected, especially around the neck and head. As the child grows, the space available for his or her legs will decrease and eventually this seat position will not be viable.
There are many reasons, based on safety, for emphatically recommending a rear-facing position until a child is at least three or four years of age. In the event of a collision, a child under 4 years of age facing forward is more likely to suffer neck and head injuries than one who is rear facing, because his or her bones and ligaments are still developing. In addition, a child's head is larger in proportion to his or her body than that of an adult, and the neck muscles take longer to support the head securely if a collision takes place.
THE SAFEST SEATS: ISOFIX OR ISIZE
The safest seats available on the market are those that use the ISOFIX fastening system or the new i-Size standard (keep in mind that a complete file on i-Size is found on this very website). I-Size, otherwise known as the ECE R129 standard, is a system that, when used properly, completely eliminates car seat placement errors, as shown in the “ECE R129 study: promoting ISOFIX but also improving the fixation of CRS with the seat belt”, by Philippe Lesire, presented at the 13th International Conference in Munich, Germany in December 2015. This standardized system is supported by UNECE in a document entitled “R129 i‐Size UN Regulation: An important step towards enhanced child protection in crashes”.
It should be kept in mind that child car seats that are now on the market and that meet current standards offer a perfectly acceptable safety level for children, regardless of the fastening system they use. In other words, we emphasize that a seat that is fastened down in a car by means of seat belts offers unquestionable safety.
However, as is well known, the major source of risk with child restraint systems involves the placement or installation of the device. A CRS (child restraint system) that is fastened with seat belts is more likely to be placed poorly or incorrectly. The variation among CRSs and seat belt-based fastening systems is so great that overall results fall quite short of the ideal, and that is why ISOFIX systems exist, as well as the more recent i-Size standard, which improves upon the ISOFIX system.
HOW DO YOU INSTALL A REAR-FACING CRS?
In general, the placement of a rear-facing CRS using ISOFIX or i-Size presents no difficulties at all. Once the base has been correctly installed, all you have to do is place the CRS in the rear-facing position. It is always important to make sure that all the parts are properly installed. A complete manual of instructions can be found here.
If the child restraint system does not have the ISOFIX feature, the rear seat belts are used. There is no single way to do this. However, the instruction manual of the child car seat should describe the installation process step-by-step. If the car seat does not come with instructions and the salesperson cannot instruct you on how to install it, you should look for a different car seat that describes in the greatest possible detail how to install the seat correctly using the seat belts.
Basically, there are several ways to fasten a CRS in a rear-facing position using a seat belt, many of which are discussed in the previously-mentioned study by Philippe Lesire et al.: The first method consists of passing the lap portion of the seat belt over the frame of the CRS (and therefore over the child's legs, without touching them), and using the diagonal, or chest, portion of the seat belt to fasten down the back part of the seat back; the second method consists of passing the lap belt through the lower part of the CRS, which is designed for this method, with the diagonal part of the seat belt holding down the back of the car seat, as in the previous case.
(Cuadro del trabajo “ECE R129: promoting ISOFIX but also improving the fixation of CRS with the seatbelt”, de Philippe Lesire)
Another method involves anchoring a base which, in turn, holds the CRS in place, but the base in question is fastened down with the seat belt. The remaining method is to use an ISOFIX or i-Size anchoring system. Of all these options, the one that offers the greatest safety by avoiding possible installation errors is the last one: ISOFIX or i-Size.
The recommendation is very clear: before buying a child car seat that does not have ISOFIX or i-Size, evaluate the option of installing one of these systems; if that is not a viable option, try to learn the best you can how to install the seat by consulting the manual, making sure that the seat belt is threaded through all the safety rings and, of course, maintaining proper tension on the seat belt itself and fastening the belt in the right position. And do not forget: it is of utmost importance to purchase your car seat at an establishment that you trust, whose sales personnel know how to answer your questions, will help you install the seat the first time, and will accept returns if necessary.