Parents may be doing more harm than good when their children pass out by performing "dangerous" manoeuvres, researchers have said.
While it is common for children to lose consciousness, parents do not always use the recovery position, which helps keep the airway open, they said.
The study of 533 parents from 11 children's emergency care departments across Europe was published in the journal Archives of Disease in Childhood.
The children ranged from babies up to the age of 18 and had either passed out within the previous 24 hours or were unconscious when they arrived at the A&E department.
In 145 cases, parents put their child in the recovery position (26% of the total).
But in 53% of cases, other manoeuvres were used - with 17% of these regarded as "dangerous".
Children were shaken in 91 cases (17%), including babies under one - for whom shaking can cause severe brain injuries.
Young babies were shaken in 25 out of 82 (31%) cases, and in 18 of these cases (22%) the shaking was considered potentially dangerous.
Among the children, loss of consciousness was most commonly caused by seizures linked to a high temperature, followed by seizures for other reasons.
One in five children had an underlying condition, the most common of which was epilepsy (7%).
Almost half had passed out on at least one other previous occasion.
The length of time the child was unconscious ranged from two to 20 minutes.
Evidence suggests that around 15% of children will have lost consciousness before they reach the end of their teenage years.
Putting the child in the recovery position was associated with a 28% overall lower risk of hospital admission, the study found.
For children under the age of two, this risk was 10 times lower.
But manoeuvres deemed to be potentially dangerous were linked with a more than doubling in the risk of requiring hospital admission.
The study was led by Dr Luigi Titomanlio, from the Robert Debre Hospital in Paris.
Alan Weir, head of clinical services at St John Ambulance, said: "All people should learn the recovery position - it's very simple and can be the difference between life and death in an emergency.
"It's crucial that an unconscious but breathing person be positioned in a way that keeps them physically stable with their airway open.
"To put someone into the recovery position, you need to kneel next to them on the floor, and place their arm nearest you at a right angle to their body, with their palm facing upwards.
"Take their other arm and place it across their chest so the back of their hand is against their cheek nearest you, and hold it there. With your other hand, lift their far knee and pull it up until their foot is flat on the floor. Carefully pull on their bent knee and roll them towards you.
"Check that their airway is open, so they can breathe and any fluid from their mouth can drain away. To do this, tilt their head back, gently tilt their chin forward and make sure that their airway will stay open and clear. Call 999 for an ambulance.
"For a child under the age of one, cradle the baby in your arms with their head tilted downwards. Holding them in this position will keep their airway open and stop them choking on their tongue or breathing in any vomit."