Kids bikes are sized based on the diameter of the wheel, they range from 12 to 24 inches before they are probably ready to try a small adult-sized bike. If you aren’t sure what size they will need, have them sit on a few different sizes to see what would work best. You want them to be able to comfortably reach the handlebars and be able to touch their toes to the ground when they’re sitting on the seat.
They should also be able to straddle the top tube of the bike (the part of the frame between the seat and the handlebars) without having their groin touching the top tube. If when the seat is at the best height for your kid, it is raised as high as it will go, it’s probably best to look at the next size up as that bike probably won’t last them very long before they grow out of it.
Proper seat height
If you’re an older kid or an adult, proper seat height means that when you’re sitting on it and the pedal is in the 6 o’clock position, you want to maintain a slight bend in your knee but not have the joint straighten out completely as you pedal. However, younger kids are usually most comfortable when they can safely touch the ground. You can start with the seat at the height they feel most comfortable with and gradually raise it up so they can get proper leg extension as they become more and more at ease on their bike.
If your kid appears to be in between sizes and is still getting comfortable riding their bike, it’s usually best to go with a bike that’s a little bit too small versus one that’s a bit too big as smaller ones will be easier for them to handle as they develop their skills.
When shopping for a bike, try prioritizing the quality of the bike versus the bells and whistles that come with it (not literally). Most kids ride their bikes in a single gear and don’t need any suspension (shocks) but a good quality, simple bike can be reused as younger kids grow up or more easily resold.
Buying a new bike for your kid every time they have a growth spurt can be expensive but there are more cost-effective used bikes available on Craigslist, Kijiji and Facebook Marketplace. You can also speak to the people in your neighbourhood about swapping bikes if the sizes work out.