For both the 5 to 9 and 7 to 10 age groups it really depends on what bike has the more appropriate stand over height seat height.
Dirt bike sizes.
Typically 17 to 21 seat height 50cc 70cc 80cc 90cc dirt bikes.
This is due to the fact that different kids have different body types sizes and length.
This is a dirt bike sizing chart guide please keep in mind that a pit bike is a dirt bike with smaller tires usually 10 or 12.
As the rider improves the throttle can be adjusted to increase performance.
Dirt rider is working on measuring 50cc 85cc and 110cc dirt bikes in house so keep an eye out for those published stories to find out the real measurements.
My article on finding the best trail bike might also be useful in your dirt biking quest.
These bikes have all of the same controls as a full sized adult dirt bike.
Between 8 and 11 years old kids will be able to use a standard gear box so a 65 cc mini dirt bike will be the best choice.
Generally speaking the cc s affect the power and smoothness of your ride but are not necessarily a measurement of power.
A 50cc bike is an ideal size for kids aged between 3 7.
Typically 21 to 28 seat height 50cc 110cc dirt bikes.