Can my 4 year old use this

Hi Angela, thank you for your inquiry, the harness forward-facing does have a limit of 29.4 kgs so you can keep him in harnessed booster mode for a little bit longer, after they have reached the weight limit there is no option with this seat it would need to go into booster mode, do you have a local store you could pop into and have your child fitted? they will be able to tell you if the seat will be suitable in booster mode for your child. We hope this helps. If you follow the link https://www.babyonthemove.co.nz/store-locations/ this will take you to our online store finder. Here you can find contact details for your nearest Baby On The Move Store where one of our team experts will be happy to assist you in your product search and help answer any further questions you may have.