Final answer:
A child is required to be in a child restraint device, which varies by age, with children aged 0-2.5 years needing a rear-facing car seat and older children transitioning to appropriate restraint systems until they fit adult seat belts.
Step-by-step explanation:
A child is required to be in a child restraint device (car seat) depending on their age and sometimes their weight or height, as per the regulations set forth by government and transportation authorities. For young children, especially those ages 0 to 2.5, it's universally recommended for them to be in a rear-facing car seat as it provides the best support for their developing spine and neck during an impact. As children grow, the type of required child restraint system changes to accommodate their size and weight - they typically transition to forward-facing seats and booster seats accordingly.
Exact requirements can vary based on jurisdiction, but general safety guidelines state that up until around the age of 6, children should be in some form of car seat. Beyond that, up until they're big enough to properly use an adult seat belt (which is often not until they're 13 or older), they should be using a booster seat.