Although the advertised inbuilt harness weight it 18 kg, the crash test dummy they use is 22 kg. They say to 18 kg because it gives a leeway for parents who do not often weigh their children. I kept my now 7 yr old in her maxi rider harness till she was 20.5 kg, mind you she was 5 yrs old to. But it is up to you if you feel safe with him in it above the advertised weight limits.

My youngest won't break 18 kg till prob 5 years. She is 2.5 years now and only 12.5 kg. But will stay in an inbuilt harness till about 20 kg.