Air bags.
Air bags can save your life. Never assume air bags replace seat belts. They work best when everyone is buckled and children are restrained in the back seat.
To do its job, an air bag comes out of the dashboard at up to 200 mph. Thus, its force can hurt those who are too close to it. Drivers can eliminate any air bag danger to children by placing children properly restrained in the back seat.
Note that many vehicles have the option of turning off the air bag when a child is present.