Children's bicycles are primarily divided by wheel size in inches, from 12" to 26".
When choosing a bike size, we primarily base our decision on the child's height or the inside length of the leg (from the crotch to the ground). We only take the child's age into account, as this is not a decisive criterion.
Inseam / Inside leg length

Feet
Children need to be able to reach the ground with both feet, as they start running while sitting, and they need to be confident that they can stop and dismount safely at any time.

Reach
An important element of fit is reach. You need to make sure that they can not only comfortably reach the handlebars with both hands, but also the brake levers - and that they can operate them easily.
All our bikes are equipped with brake levers with adjustable reach.

What if the child is between sizes?
While it's tempting for parents to go for a larger size, it's better to go for a smaller size for a child's bike. Why?
A larger bike is harder for a child to steer, stop, and start, especially if they have to stand on their toes to reach the ground. A larger bike can feel intimidating and less comfortable, especially for complete beginners.
Since a sense of control, safety, and confidence are key to a pleasant riding experience for children, it's clear why a smaller bike is likely to offer a better experience.
The exception is when a children's bike bought in the fall (Christmas) but realistically the child will ride until spring, and that span can be up to half a year. If the child is already on the size limit in the fall, it is advisable to consider a larger size, but you just need to keep in mind a very simple rule:
