Children can stop using car seats for their safety when they reach the height and weight limits as well as age.
A toddler should remain in a regular 5 point harness car seat until they are at least 4 years old as long as they can fit in the child car seat.
After 4 years old the child can usually move up to a booster seat which raises their body up high enough for the cars seat belt to fit them properly.
If the child is still too small for the seat belt of the vehicle to fit them properly even with a booster seat then they should remain in the car seat with the harness until they are big enough.
Then when a child moves to a booster car seat they should remain in the booster seat until around age 8 to 12 years old.
Children 12 and under should also ride in the back seat because of the airbags that could injure or kill the child.
Once they turn 13 years old they can ride in the front seat.