Like Jodi, we bought a maxi rider for Jack - your DS should be able to go in that, I think the minimum weight is 12 kgs. I know of many others with a small gap who have bought a maxi rider for the older child. The reason is that it will last a long time as it can also be used as a booster seat when they are bigger, and it is one of the safest booster seats as you can an anti-submarining clip (goes between the legs to stop them slipping down).