The beginner's guide to buying a car seat - from four years

By the time your child reaches his fourth birthday, things will doubtless be getting a little snug in the strapping-into-car-seat department (unless you've been clever/rich enough to buy a Group 1/2/3 car seat, in which case he won't feel snug for a long time yet and you can feel smug instead).

But that doesn't mean you can chuck out the car seat and chuck him onto the back seat with nothing but the adult seat belt to hold him in. It is now a legal requirement that all children must travel in an 'appropriate' car seat until their 12th birthday or until they are 1.35m tall (whichever comes first). 'Appropriate' in your older child's case usually means a booster seat (with or without a back support), which will lift him high enough to fit the adult seat belt safely – and, happily, give him a much better view out of the window. 

Safety | Weight categories | Portability | Installation | Comfort | Value for money | Car seats and the law

Safety
As with all car seats, you need to check that the booster seat you're thinking of buying has an E Mark on it (confirming that the seat conforms to all the officially required safety standards).

Thankfully, most booster seats tend to fit securely into more makes of car than your average baby/toddler car seat but it's still worthwhile checking that your car is on the booster-seat-manufacturer's list of compatible car models. Even then, you really should test the fit of the booster seat – with your child in it – before you buy it. Check that:

• The adult belt can be worn as tightly as possible.
• The lap belt goes over the pelvic region and not across the stomach.
• The diagonal strap goes over the shoulder and not the neck.
• The belt is flat and that there are no twists.

Although it is legal for a child over three to travel (in a car seat) on the front passenger seat, it's still safer to put the booster seat on the back seat.

We do not ask members who review car seats to rate them for safety, as – thank goodness – most people do not get to test this particular feature first-hand. However, we would encourage members to check the latest safety reports and contact the manufacturer direct if they have any specific safety concerns.

Weight categories
Remember that (supremely unhelpfully) child car-seats are categorised into groups by numbers and symbols, rather than by weight of the child they should contain. So, this time round, you're looking for a Group 2/3 seat, suitable for children weighing 15 to 36 kgs (roughly four to 11 years).

If the car seat you bought your baby at about nine months is a Group 1/2/3 combination seat, you don't need to buy another one: you're all set to travel safely for the next seven years. The only drawback with a combination seat like this that it's usually trickier and heavier to move from car to car.

Portability
Most Group 2/3 seats are pretty lightweight and can be moved from car to car with ease. The backless booster seats are often compact enough to be carried on a train or as hand luggage on a plane. They're also useful as spare seats. As one Mumsnetter says, "We always keep a Mothercare booster in the boot in case we are giving my kids' friends a lift." 

Installation
If you still getting sweaty flashbacks from the first time you tried to fit your infant car seat into the car for the first time, then the good news is these seats are much easier to install. Because they use the car's own seatbelt, it's usually a matter of just strapping the child in as you would yourself, although most models have a 'belt guide' which the belt is threaded through and ensures a good fit. Some seats have strap slides which secure the seatbelt further. 

Comfort
For long journeys, seats with backs and head rests are great for preventing heads from lolling about or falling forward as your child sleeps. Many models have extendable headrests which 'grow' with the child - a great concept when you think of the height difference between a four-year-old and an eleven-year-old. There are even model offer padding, arm rests, side wings and (a big hit with most kids) cup-holders. 

Value for money
Group 2/3 seats do vary in cost, depending on their size, shape and extras. It's obviously tempting to go for one of the cheapest models but, before you do, remember that this seat will last your child a long time, so it may be worth paying a bit more if you think you'll need it. And, of course, do remember that you should never buy any car seat secondhand, unless you know its complete history and are sure it's never been involved in an accident. 

Car seats and the law
According to the car-seat law regulations that came into force in 2006, it is the driver's responsibility to check that children travelling in her car are "correctly restrained". You should know, then, that:

• It is illegal for a child over three and under 12 (or 1.35m tall) to travel in the front or back of a car, unless the child is strapped into car seat that is suitable for her size. The only exceptions to this rule are: travel by taxi or licensed hire car where there is no appropriate child restraint available (in which case, the child must wear the adult seat belt); a short, unexpected but important journey where there is no appropriate child restraint available (in which case, the child must wear the adult seat belt); the presence of two other occupied child car seats on the rear passenger seat that prevent fitment of a third seat (in which case, the child must wear the adult seat belt); and travel in a car with no adult seat belts fitted (in which case,  the child should travel unrestrained in the rear).

The legal regulations are slightly different for children over the age of three (find them here) but all children must still travel in an appropriate car seat until either their 12th birthday or they are 1.35m tall.