When you brake sharply, your heads are thrown forward, which could potentially damage your childs neck, whereas if they are in a rear facing, their head will be thrown backwards and supported by the seat behind them...
In the US, they recommend rear facing until age 2 or (I believe) 40 lbs. Supposedly they settled on the weight because the 99th percentile for a 2 year old is 35 lbs.
This has just recently gone up. The general suggestion before was age 1 or 25 lbs.
I'm not sure why it is, but I do know here in US its recommended to rear face until at least 2 years old because a child 2 and under is 75% less likely to die in an accident when rear-facing
Many car seat rear face longer than 2 years old depending on childs weight, look around for one that does
Here are some videos that show why it's actually safer to be RF
It's actually safer for everyone to be RF but obviously that isn't possible. The longer they RF the better. I turned my son at 3yrs old because no matter how tight his harness was he was a little houdini and was able to get out of it, so we made the decision that it was safer for me to be able to see what he was doing before he was out of his seat. My personal minimum would be 2yrs old. The recommendation here in the US is now 2yrs or outgrowing a convertible car seat-weight limit on them are 35-45lbs.
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