In Sweden it is common to use rear-facing seats up to age four
Most UK parents are too quick to switch their children to front-facing car seats, a team of doctors has argued.
They say mounting evidence suggests it is safer for children to use a rear-facing seat until the age of four and parents should be advised accordingly.
In the UK it is common practice to switch babies to a front-facing seat when they weigh 9kg (20lb) - around the age of eight months for an average boy.
The study, in the British Medical Journal, was backed by safety experts.
Dr Elizabeth Watson and Dr Michael Monteiro cite evidence from Sweden, where using a rear-facing seat up to the age of four is common practice.
There, studies have shown that children who died in accidents restrained in a forward-facing booster seat could potentially have survived if they had been travelling in rear-facing seats.
Another study used the US National Highway Traffic Safety Administration database to examine crashes involving 870 children between 1998 and 2003.
It concluded that rear-facing seats were more effective than forward-facing seats in protecting children aged 0-23 months for all crash types.
Recent crash tests have also reported that rear-facing seats resulted in significantly lower neck and chest injury measures compared with forward-facing seats.
Dr Watson said: "Rear facing car seats cradle a child in an impact with any frontal component, and align the head, neck and spine, spreading the crash forces over all of these body areas.
"In a forward facing car seat, a child's body is held back by the straps, while the head keeps moving forwards, and the relatively large head mass and differences in the cervical spine in young children can lead to excessive stretching of the spinal cord."
She added that many parents and healthcare providers may be unaware that it is safer to leave children in rear-facing seats for as long as possible - or that rear-facing seats for toddlers exist.
She said healthcare professionals should advise that rear-facing seats are safer than forward-facing seats for children under four years.
She also called on manufacturers and retailers to make rear-facing seats for older children more available.
And she criticised the current weight-range labelling of European seats, which they said might imply that forward-facing seats are as safe as rear-facing seats for children over 9kg.
Duncan Vernon, of the Royal Society for the Prevention of Accidents, backed the findings.
He said: "The evidence shows that it is safer for children to travel rearward-facing for as long as possible, although that does not mean forward-facing seats are dangerous."
Mr Vernon said parents should not be tempted to switch to a forward-facing seat as soon as their child reached the minimum weight.
He called for greater availability of rear-facing seats in shops, so an expert could provide advice on how to fit it.
Relying on ordering a seat over the web ran the risk that it would not be fitted properly, and so put the child at risk, he added.