By law in Canada, a child must be 40lbs before using a booster. How old is he?
Does he still have room in his current seat?
Here is some information for booster use:
http://peicarseatsafety.ca/booster/
Here are questions to ask yourself before moving to a booster:
To determine if your child is ready for a booster, ask yourself:
Does your child meet the weight, height and age requirements of the booster?
Can your child sit in the booster correctly each and every trip, not slumping over or leaning out of position?
Will your child leave the seat belt positioned correctly (not putting seat belt behind back)?
Also, if they are known to sleep in the vehicle, can they stay in position while asleep?
If you have answered no to any of the above questions, then your child is not ready for a booster seat. If they have outgrown their existing seat, there may be other seats available to keep your child harnessed to a safe booster age.