Final answer:
The mandatory requirement for toddlers weighing 9-18 kg during car travel is to use a forward-facing car seat with a 5-point harness.
Step-by-step explanation:
The mandatory requirement for toddlers weighing 9-18 kg during car travel is to use a child car seat. Child car seats are designed to provide proper restraint and protection for young children in vehicles. They are categorized into different types based on the child's weight and age.
For toddlers in the weight range of 9-18 kg, a forward-facing car seat with a 5-point harness is recommended. This type of car seat secures the child using a harness system with straps that go over the shoulders, across the chest, and between the legs.
It is important to choose a car seat that is suitable for the child's weight and age and to use it correctly according to the manufacturer's instructions.