Find the right wheel size for your child's next bike, based on their height or age.
It depends mainly on height rather than age, since kids of the same age can vary a lot in size — enter your child's height above for the most reliable estimate, and use age only as a rough backup if you don't have a recent measurement.
Height, by a good margin — two 6-year-olds can differ by several inches in height, which can mean a real difference in comfortable wheel size. Age-based estimates are only a starting point when you don't have a current height measurement handy.
Generally, sizing down is safer for a child just starting out (easier to reach the ground and brake confidently), while sizing up can suit a more experienced rider who's about to have a growth spurt. Test-riding when possible beats any chart.
No — frame geometry, seat height range and handlebar reach can all shift the effective fit even at the same wheel size, so treat any chart (including this one) as a starting point and check the specific bike's stand-over height and seat range against your child's inseam.
Have your child stand with their back against a wall, feet flat and about shoulder-width apart, then measure from the floor straight up to their crotch. Compare that number to a specific bike's minimum stand-over height (usually listed by the manufacturer) for the most precise fit.