When the car crashes in an accident the seatbelt allows you to come to a slightly more gradual stop than personally smacking into something else in the car. They distribute the forces to areas of your body that can better handle it like the hips and shoulder bones.  Seatbelts also stretch a little allowing for even more gradual deceleration.  In a toddler child safety seat the belts are similar to a racing harness as they are basically 5 point secured belts, which hold the child firmly in place and surround them with protection.  In a properly installed and secured child safety seat a child is quite safe. 

Infant child safety seats are now required to be rear facing so the brunt or force of most accidents are absorbed through the back and the neck can’t hyperextend due to the seat back.  This is the safest position as most serious accidents involve some degree of frontal impact.  Older child safety seats are akin to a booster seat or safety seat and may have their own belting system or incorporate the cars seat belts.  Regardless of the child safety seats or seat belts used, if they are not installed properly or used effectively they can and will fail and serious injury or death could result.  It is imperative that you seek expert advice to make sure you have your child safety seats properly installed and that you learn how to properly use them. 

Airbags are standard on all cars nowadays and are an additional safety device.  They are not an alternative for seatbelts.  They are designed to be an additional safety device further increasing the safety of the occupants by reducing bodily impact with hard and sharp edges and forward movement.  Even if your car is fitted with airbags it’s imperative that you buckle up as they can also seriously injure or even kill you if you don’t wear your seat belt.  Air bags inflate at a very rapid or almost immediate speed, if you get too close to one it can seriously injure you, if not kill you.