Make sure your child is properly restrained in their car seat before you drive, every time, without exception.
We had a recent crash in which that caveat would have saved a small child’s life. I say that not to condemn that mother, but so we don’t have to tell another mother that that is the case.
I also want to say that none of us are perfect. I remember setting out on a car trip years ago. I was an ER Doc at the time, so was acutely aware of the need for proper child restraint, but I looked in the rearview mirror and my daughter was in the process of extricating herself from her car seat. My heart leapt and I quickly pulled off the road to refasten her. I don’t know what I had done wrong the first time putting her in, but I was certain she was “in” properly from then on through her years of riding with me (She is now 18 and has been doing her own seatbelt for several years now). That vision of her “Houdiniing” was often in my mind as I did up the fastening.
The National Highway Safety Administration has a wealth of information on “highway” safety, including stuff on car seat safety with links to find someone who can inspect your child’s car seat to make sure that it is a safe one, that it is installed properly, that you understand how to use it properly, and that it has all its parts.