There are 3 stages of car seats to ensure safety for your child:

• Stage 1: Your child needs to be secured in a rear-facing infant safety seat until they are at least 13kg or 75cm, usually around 12 months old. Rear-facing seats spread the force of a crash over the larger area of the back, as opposed to the force being taken by the underdeveloped neck, when the proportionally big head of a young child is thrown forward. A bulky jacket or blanket underneath the harness can create a lot of slack between the harness and your child when the force on impact in a crash compresses the fabric. This can lead to your child being ejected from his seat. Rather place the blanket or jacket over your child once he is strapped into the harness.
• Stage 2: Your toddler and preschooler needs to be secured in a rear-facing toddler safety seat until they are at least 18kg or 105cm, usually between three and four years old. Ideally, invest in one of the two rear-facing seats available in South Africa that can accommodate children up to 25kg or 115cm. If an extended rear-facing seat is not financially viable, a high quality forward-facing seat that offers a decent recline, and easily adjustable headrests and harness, is adequate. Only once they have outgrown the weight or height limit on their rear-facing seat, should children graduate to a front-facing booster seat, which is designed to be used with the car’s built-in seatbelts.
• Stage 3: Your primary schooler needs to be secured in a front-facing, high-backed booster seat until they are at least 36kg or 1.5m tall. The booster seat provides guides to safely position the seatbelt on their still-developing body. The lower part of the seatbelt should go across your child’s pelvis, not his stomach. The shoulder belt should sit on their chest and collarbone, and not touch his face or neck, and it should never be put behind your child’s back, or under his arm. Your child shouldn’t be allowed to sit in the front passenger seat until he is 13 years old. His body is not sufficiently developed to withstand the impact of a crash in that position, and an airbag activating can seriously damage an underdeveloped body.

[https://www.livingandloving.co.za/family/car-seat-safety-law-south-africa]