My 7 year old daughter uses this while riding an MTB. Her head size is 51cm and the helmet is for 50-57cm head-szies. The fit is decent. The chin-strap lock is easy to open for kids since it is a micro-meter lock. The lock however fits right near her neck under her chin so it is a bit uncomfortable and I have not yet been able to adjust the straps to move the lock away from under her chin.