Use a child car seat: never hold a child in your arms in a moving car
In a hard stop, your arms cannot hold a child. A properly used car seat can.
What the evidence says
NHTSA estimates that properly used car seats cut fatal injury by about 71% for infants (under 1) and about 54% for toddlers (1 to 4) in passenger cars, compared with being unrestrained.
Evidence grade: A: official estimates. See how we grade evidence.
What to do
Keep children rear-facing as long as the seat allows within its limits. Check the seat's expiration date and local law. Many areas offer free car-seat inspection stations; in the US, start at the NHTSA car seat page.
Where rules differ
US, UK and EU age and height rules differ. Follow the stricter of the law and the seat manual.
Sources
Not medical, legal or financial advice. This page is general information. Talk to a qualified professional about your own situation. Emergency: 911 (US), 999 (UK), 112 (EU). Crisis support: 988 (US), Samaritans 116 123 (UK).