Final answer:
Childhood obesity is defined as having a body weight at least 20 percent higher than a healthy weight for a child of that height.
Step-by-step explanation:
The statement that provides the best operational definition of childhood obesity is:
b. Body weight at least 20 percent higher than a healthy weight for a child of that height
This statement accurately defines childhood obesity by specifying that it is a condition where a child's body weight is significantly higher than what is considered healthy for their height. This definition takes into account the relative measure of body weight and height, which is often assessed using the Body Mass Index (BMI).