Restrict for Children in Cars

Children up to the age of 12, or 1.35 m height five feet (4ft), must use safety seat on the bus. This means: the children under the age of 12 need to use a child-size chair.
Aged 0-3

This period of children with appropriate to the child restraints (see below), whether they are in front of the back seat or a car and truck or goods vehicles. Children under the age of 3 in vehicles cannot travel without the seat belt.

There was one exception - in a taxi or rented the car with a car parking sensor you children may travel free if appropriate restriction is not available.
3-12 years of age, and the height five feet (135m m 4ft)

Adult seatbelt must wear seat in front or rear, when available. It is your responsibility to ensure that the driver is correct.
14 years old and above

This period of children are considered adult passenger, so they are responsible for their own safety. They must wear seat belts, adult in front or rear seats.
Children's seat

"Children's seat is an umbrella, covering babies and children's chair, chair cushion pressurization booster seat.

Each constraint is designed for a particular weight. When choosing a, find a tag shows "E" and "44.03 'or' 03 quantity, weight or group, for children, its purpose.

The group's definition, although some manufacturers using alternative descriptive names for their products, can occasionally coverage, and overlap, weight of offer more choice.

What is the most important thing is for you, the constraint of the children. The age of only provide guidance.

Note you should never use baby seat (group) in the 0-0 with an active + seat before you can use airbags and restrictions on seat and airbags the carmaker, if you confirm it is safe, check your car manual.
Groups, + : 10/13kg (born to 9 to 12 months).

A rear-facing seats for baby or behind or in front of the car.
I: 9-18kg group (9 months ~ 4 years).

A pointer to a child-size chair use in front or rear. The child restraints and their management, especially for your child, and should include a "crotch strap, in order to avoid children sneaking in a car accident.
Second: 5-25 kg (4-6 years) or 15-36kg

A pointer to a booster seat in front or back for either with adult seatbelt. Booster seat with a back, and adding to your child, so highly accurate positioning fasten your seat belt.
The third group (6 years, 22-36kg:

A pointer to a booster seat in front or back for either with adult seatbelt. Booster seat with a back, and adding to your child, so highly accurate positioning fasten your seat belt.
The third group: 22-36kg (6).

A pointer to a booster pad ahead or behind for adult seatbelt. Booster mat, like a booster, make your children to sit for the height of adult seatbelt makes correctly.

If your child weight more than 36kg but age is still required to wear constraint, you should continue to use, because it will take more weight.
Choose a kind of constraint.