Child abuse in Kansas is a felony, but the description above is inaccurate, as only severe harms are classified as child abuse. This is the statute:

21-3609. Abuse of a child. Abuse of a child is intentionally torturing, cruelly beating, shaking which results in great bodily harm or inflicting cruel and inhuman corporal punishment upon any child under the age of 18 years.
Abuse of a child is a severity level 5, person felony.

If this corporal punishment doesn't rise to the level of "cruel and inhuman," or "cruelly beating" a child, it wouldn't be a felony, although it could probably still be prosecuted as a lesser offense. My point is that not every offense involving striking a child is a felony "no matter how minimal or severe."

You are right, but in this case the Division of Children's services found substantial evidence that this boy was abused.

In the state of Missouri, where the incident took place:

Abuse of a child, penalty:

568.060. 1. A person commits the crime of abuse of a child if such person:

(1) Knowingly inflicts cruel and inhuman punishment upon a child less than seventeen years old;

So charging the instructor with a felony was the right thing to do. Striking a child 26 times with a stick constitutes cruel and inhuman in my eyes.