Moving a child from a forward-facing restraint with an inbuilt harness into a booster seat is an important transition.
Australian law provides minimum age requirements, but age alone does not determine whether a child is ready. Their size, shoulder position, behaviour and the instructions for their current restraint should all be considered.
The safest approach is to keep a child in each suitable restraint stage until they no longer fit it, rather than moving them as soon as they reach the minimum age.
What Is the Legal Age for a Booster Seat in Australia?
Under Australia’s national child-restraint laws:
- Children under six months must use an approved rearward-facing restraint.
- Children aged six months to under four years must use an approved rearward-facing or forward-facing restraint with an inbuilt harness.
- Children aged four to under seven years must use an approved forward-facing restraint with an inbuilt harness or an approved booster seat.
- Children aged seven and older may use an adult seatbelt, but should continue using an appropriate child restraint or booster if the seatbelt does not fit them correctly.
This means a child must not move into a booster seat before turning four.
However, turning four does not automatically mean they should move. If the child still fits correctly within their current harnessed restraint, they may be able to remain in it until they reach its upper shoulder-height marker.
Use Shoulder-Height Markers, Not Age Alone
Approved Australian child restraints use shoulder-height markers to help parents determine when a child can begin using the restraint and when they have outgrown it.
Before moving a child into a booster seat, check the upper marker on their current harnessed restraint.
Depending on the product instructions, a child may be ready to transition when:
- Their shoulders have passed the upper shoulder-height marker
- Their shoulders no longer fit comfortably within the restraint
- Their eye level is higher than the back of the restraint
- The highest available harness position is below their shoulders
Always follow the instructions supplied with the specific restraint. The product’s shoulder-height markers take priority over general age ranges.
Harnessed Restraint or Booster Seat?
A forward-facing restraint with an inbuilt harness holds the child using a harness that forms part of the restraint.
A booster seat works differently. It raises and positions the child so the vehicle’s lap-sash seatbelt can sit correctly across their body.
A booster seat does not usually provide an inbuilt harness. The vehicle seatbelt becomes the system that restrains the child.
For this reason, a child using a booster must be able to remain seated correctly for the entire journey.
Signs Your Child May Be Ready for a Booster
A child may be ready to move into a booster seat when:
- They are at least four years old
- They have reached the appropriate shoulder-height marker
- They no longer fit correctly in their current harnessed restraint
- They meet the booster seat’s entry requirements
- They can sit upright without leaning, slouching or moving the seatbelt
- The vehicle has a suitable lap-sash seatbelt in the intended position
- The booster can be installed and used correctly in the vehicle
All of these factors should be considered together.
A child who meets the minimum age but still fits their harnessed restraint does not need to move simply because they have turned four.
Signs Your Child May Not Be Ready
Your child may not be ready for a booster if:
- They are under four years old
- Their shoulders have not reached the booster seat’s entry marker
- They still fit appropriately in their existing harnessed restraint
- They regularly lean forward, slouch or move out of position
- They place the sash belt under their arm or behind their back
- The lap belt sits across their abdomen
- The intended vehicle position does not provide the required seatbelt or anchorage
- The booster does not fit correctly within the vehicle
If the child cannot remain correctly positioned, continuing with a suitable harnessed restraint may be the more appropriate option.
How Should the Seatbelt Fit in a Booster?
The purpose of a booster seat is to improve the position of the vehicle seatbelt across the child.
When correctly positioned:
- The sash belt should cross the middle of the shoulder
- The sash should sit across the chest
- The lap section should sit low across the hips and upper thighs
- The belt should lie flat without twists
- The child should sit upright and remain in position
The sash belt should not cut across the child’s neck or face.
The lap section should not sit high across the abdomen. The child should also never place the sash belt under their arm or behind their back.
Always use the booster’s sash guide, lap-belt path and other positioning features as shown in its instructions.
Does a Booster Seat Need a Top Tether?
Some Australian booster seats require a top-tether strap, while others may have different requirements.
If the booster is supplied with a top tether and its instructions require it, the tether must be connected to the correct child-restraint anchorage and adjusted as directed.
Do not assume that a booster can be used without a tether based on another model you have used previously.
Check both the booster-seat instructions and vehicle owner’s manual before installation.
What Type of Seatbelt Does a Booster Use?
Children in booster seats generally need to be restrained using a suitable lap-sash seatbelt that is properly positioned, adjusted and fastened.
A lap-only seatbelt does not provide the same upper-body positioning.
Do not use a booster with a lap-only belt unless the particular set-up is permitted by the restraint instructions and uses any additional approved equipment required.
If you are uncertain about the available seatbelt, ask the manufacturer or an authorised child-restraint fitter before using that seating position.
When Can a Child Stop Using a Booster?
Turning seven does not automatically mean a child is ready to use an adult seatbelt without a booster.
A height of approximately 145 centimetres is commonly recommended as the minimum point at which an adult lap-sash seatbelt may begin to fit correctly. Vehicle seats and children’s proportions differ, so height should be considered alongside actual seatbelt fit.
Use the five-step test. Without a booster, the child should be able to:
- Sit with their back against the vehicle seat.
- Bend their knees comfortably over the front edge of the seat.
- Position the sash belt across the middle of their shoulder.
- Position the lap belt low across the top of their thighs.
- Remain in this position for the entire journey.
If the answer to any step is no, the child may still need an appropriate booster seat.
Seatbelt fit should also be checked in every vehicle. A child may fit correctly without a booster in one vehicle but still need one in another.
Common Booster-Seat Mistakes
Common mistakes can include:
- Moving a child into a booster as soon as they turn four
- Removing the booster as soon as they turn seven
- Ignoring shoulder-height markers
- Using a lap-only belt where it is not permitted
- Allowing the lap belt to sit across the abdomen
- Allowing the child to place the sash under their arm
- Routing the seatbelt outside the booster’s guides
- Using the wrong vehicle anchorage
- Assuming the booster fits every vehicle
- Allowing the child to slouch or lean during travel
Regularly check the restraint as the child grows and whenever it is moved into another vehicle.
Choosing the Right Booster
When comparing booster seats, consider:
- The child’s current shoulder height
- The booster’s entry and exit markers
- Seatbelt positioning
- Head and side support
- Vehicle-seat compatibility
- Top-tether requirements
- Available space beside other restraints
- Whether the child can use it correctly on every journey
InfaSecure offers harnessed restraints and booster seats designed for different stages of childhood. The right choice will depend on the individual child, vehicle and seating position.
The Most Important Rule
Do not rush the transition between restraint stages.
Keep your child in their current approved restraint for as long as they fit within its permitted limits. When they do move into a booster, make sure the booster suits their size, fits the vehicle and positions the seatbelt correctly.
Always follow the child-restraint instructions and vehicle owner’s manual. If you are unsure, contact InfaGroup Customer Care or arrange an assessment with an authorised child-restraint fitter.
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