The size bike you choose should be determined by the leg length and height of the child , rather than age, as this is the most reliable way of getting the right size of bike for each child. Age alone isn’t a reliable measure as there is a large spread of “normal” leg lengths & heights for each age.
Most bikes have decent length seat posts, so the saddle can be raised a long way as the rider grows.
We recommend that you come into your LBS in Knysna who will have many of our bikes in store so the rider can sit on a bike. You will get help and advice on sizing, and get on-going service, as well as support.
Approx age/size – but remember it depends more on the size of your child AND their confidence
2-3 12” pushbike
3-5 16” wheel size
5-7 20” wheel size
8-10 24” wheel size
9-12 26” or 27.5” wheel size in a XS or S frame