When do you start to use booster seat with your child?

Your child's weight is usually the best guide to deciding when to use a booster seat. If your kid is over 15 kgs she can be in a booster seat and continue to be in it till she is 36kgs. A large number of kids reach this milestone around their 4th birthday. However if your child still fits comfortably in the car seat, which means her shoulders are below the top set of harness-strap slots in the car seat's back -- carry on using the car seat.