Car seats! Properly securing an appropriate car seat is vital to the child's safety. Safe driving practices are obviously essential too!
Car seat safety. This is the big answer to this question. Under 40 lbs needs a forward facing 5 point restraint car seat that is properly installed. Have a local agency specializing (i.E fire station) in car seat installation and get yours checked out. Make sure the straps fit correctly and are at the right height. Lastly, make sure your car is in good working order and safe for the kids to ride in.
Couple suggestions. Your preferred plan is for baby to face the face the rear window in a convertible car seat. It is acceptable to forward face after two years old if over 20 pounds but i recommend they rear face to the seat's rf weight limit. Never leave a child alone in a car while you run an errand. You could lose your child to a thief or heatstroke.