*When you start looking into car seats it is easy to look at test reports and make instant decisions about particular brands or seats.
*The standards do not allow companies to make 'substandard' seats - many of the differences between cheaper seats and the more expensive models are the ease in which they can be fitted in the car and the range of cars that they will fit.
*So now we know child car seats meet a set standard now comes the difficult part, not all seats are compatible with all cars - it is important to check which seat fits in your car.
*The highest rated seats in a magazine test report could be the worst fitting seat in your vehicle, putting your baby or child at high risk from injury.
Stage 0+ Infant Carriers
These seats take your baby from newborn to around 1 year - it is the weight of your baby that determines which seat must be used, nothing to do with baby's leg length, the zero plus seat will take your child to 13 kilograms or 28lbs. Some fine boned little girls could reach 18 months or 2 years before meeting this weight.
Rear Facing Seat
While using this stage seat your baby will always face the rear of the car - this ensures that during an impact baby will be forced into the seat, then on the recoil the baby and the seat will remain together - the seat shell will support and protect baby.
If the seat has been involved in an accident it must be replaced as it may have sustained damage not visible to the naked eye, the harness is designed to stretch preventing it from damaging internal organs, this can only happen once so any subsequent impact would leave the harness with no more stretch and could harm baby.
It is for these reasons that you should never be tempted to purchase or borrow a second hand car seat.
Stage 0+ and 1 Car Seats
These car seats are much larger seats, designed to protect your baby from newborn to around 4 years - when used for a baby up to 9kgs, the seat is used rearward facing, once baby has reached that 9 kg weight the seat can be turned round and is used forward facing - baby does not have to be forward facing until he/she is 13 kgs. When purchasing this style of seat you must check that it is compatible with your vehicle when fitted forward and rearward facing.
This style seat will remain in the car even when being used with a tiny baby because they are too heavy to move easily. This may result in you constantly waking your sleeping baby, but they will fall asleep again quite quickly - you must never be tempted to leave baby asleep unattended in the car.
Stage 1 Child Car Seat
The stage one child car seat will take baby from 9 kgs to 18 kgs this is from around 1 year (this age is only as a guide baby must weigh 9kgs) to around 4 years in a forward facing position. These will generally need to remain in the car as they are heavy, and need to be fitted taking great care to follow the seat belt routings and tighten well. They can also be car specific for correct fitting, not every seat fits every car. If you have two cars it might be better to purchase two seats, each one fitting the car perfectly rather than buying one seat that only fits each car satisfactorily.
Stage 2 Child Car Seat
This seat takes your child from 15kgs (33lbs) to 25kgs (55lbs), from around 4 to around 10 years depending on the Childs height and build. If your child is over the 25kgs weight but is below 135cm in height it is recommended that the child remain in the seat. The majority of Stage 2 seats have a height adjustable back to allow you to gradually change the height of the back as your child grows; this also changes the height and angle of the seat belt, keeping it constantly in the optimum safest position.
These seats do not have to be fitted to each car and will generally fit all vehicles without too many problems - sports car owners with bucket seats will need to choose a seat with a small base.
Stage 1 & 2 Child Car Seat
A number of seats are now available to cover from 9kgs to 36kgs this will take a child from around 1 year to 12 years; the seat is supplied with a harness or a lock off for the adult seat belt. The harness or lock off continues to be used until between 15Kgs and 18kgs, then the seat is used with the adult seat belt 'free running' as used by yourself. The back of the seat will continue to adjust in height, and in some cases width. These seats are generally designed to be used until the child is 135cms in height or 12 years.
Stage 3 Child Car Seats
This stage is not recommended until 22kg or 6 years, it has no side protection and just raises the child to a height that will allow the adult seat belt to sit in the correct position, some do have a clip to help with this problem.
ISOFIX Fitting Car Seats
Many cars but not all are now being produced with Isofix fittings (these are not standard and even though the salesman and hand book may refer to them they may not be fitted, so always do a manual check). These fittings are a pair of bars attached to the chassis of the car at the time of manufacture and cannot usually be retro fitted. This system will give you the opportunity to simply click the child car seat into the fittings without worrying about whether you have the seat belt routings correct or the belts tightened enough.
The Isofix child seats are categorised in three groups - it is important to check the compatibility with the child car seat manufacturer as to which seat you can used in your vehicle before making any buying decisions.
(Source:http://www.olivers-baby-care.co.uk/help-advice/car-seats-travel.asp)