Every move to the next seat feels like a milestone. But each one gives your child a little less protection in a crash. Here's what changes at the three big moves, and the earliest age and size for each.
Go by your child's height and weight, not their age. Our recommendation is to keep your child rear-facing, or at least in a harness, until 125 cm or 25 kg. That means choosing a seat rated that far.
"Harness" means the seat's own 5-point straps: two over the shoulders, two at the hips and one between the legs. Infant carriers, rear-facing and forward-facing seats all use one. A booster has no straps; it uses the car's adult belt.
| The move | Our recommendation: move up at | Typical age (average child) | At the very least (standard seats) | Earliest allowed (EU) | Main risk if too soon |
|---|---|---|---|---|---|
| Infant carrier to extended rear-facing | When the head is within 2.5 cm of the top of the shell, or past the carrier's limit | About 1 to 1½ years | Carrier's limit (often 75–87 cm, 13 kg) | No minimum | Head above the shell |
| Rear-facing to forward-facing | 125 cm or 25 kg, in a seat rated to rear-face that far | About 7 to 8 years | Past both 105 cm and 18 kg (about 5 years) | 15 months and 76 cm | Head and neck injury |
| Harnessed seat (rear- or forward-facing) to high-back booster | 125 cm or 25 kg, in a seat rated to harness that far | About 7 to 8 years | Past both 105 cm and 18 kg (about 5 years) | 100 cm | Tummy and spine injury, or slipping out of the belt |
| Booster to adult belt | 150 cm, and the belt fits | About 11 to 12 years | The legal limit (next column) | Belt across the neck and tummy | |
| Back seat to front seat | 150 cm and about 12 to 13 years | About 12 to 13 years | The legal rule (next column) | Being hit by the airbag |
Typical ages are based on WHO growth figures for an average child. Smaller or lighter children reach these sizes later, sometimes a year or more, and bigger children earlier, so always measure.
Why these numbers: most standard rear-facing and harness seats in Europe are outgrown at 105 cm or 18 kg, whichever comes first. A booster needs your child past both; if they outgrow one limit first, move to a bigger harness or rear-facing seat, not a booster. Seats rated to 125 cm and 25 kg exist, and let most children stay rear-facing or harnessed until about age 7. Our recommendation, based on seat limits and expert guidance; always check your seat's label.
Coming soon: our shortlist of extended rear-facing and extended harness seats, with test results and the best EU price.
Most serious crashes are head-on. In a head-on crash, everything in the car keeps moving forward.
Best thing you can do: choose an extended rear-facing seat rated to 125 cm and 25 kg, and keep your child rear-facing until they reach it. Most children get there around age 7. Standard rear-facing seats stop at about 105 cm and 18 kg, so check the label before you buy. Rear-facing to these sizes is normal practice in Sweden.
A harness holds your child at the shoulders and hips with five straps. A booster has no straps of its own. It only lifts your child so the car's adult belt fits. If your child is too small, or can't sit still, the belt ends up in the wrong place.
Why European children often move to a booster young: many harness seats sold in Europe stop at 105 cm or 18 kg, which an average child reaches around age 4 to 5. Seats with higher harness limits (up to about 25 kg or 125 cm) let you keep a harness for longer.
Best thing you can do: keep your child in a rear-facing or harness seat until 125 cm or 25 kg. At the very least, wait until they're past both 105 cm and 18 kg. They should also be able to sit upright with the belt in place for the whole trip, even asleep.
Best thing you can do: rear-facing first, then a forward-facing harness, then a booster. Don't use a booster for a child who is small, light or can't sit still the whole trip, however old they are.
So a booster can work as well as a harness, but only for a child who is big enough for the belt to fit and mature enough to stay in position. For younger, smaller or lighter children, the harness is safer.
Front airbags are made for adults. They burst out of the dashboard in a fraction of a second, with enough force to injure someone sitting close to them.
Best thing you can do: keep your child in the back seat until about 12 to 13 years old.