Using the 2017-2018 National Health and Nutrition Examination Survey (weighted population size = 35,460,209; 8-18 years old; 52.1% males), we compared the obesity prevalence in children and adolescents between body mass index-based (BMI-based) and total percent body fat-based (BF%-based, measured by the dual-energy x-ray absorptiometry) cutoffs. The BMI-based cutoffs exhibited closer alignments (k, 0.88-0.97) in the childhood obesity prevalence, while the absolute (sex-specific) BF% cutoffs had higher prevalence rates than the relative (age- and sex-specific) BF% cutoffs (k = 0.43 [95% CI, 0.38-0.49]), overly labeling Non-Hispanic white and Other race/ethnicity females with obesity. The BF%-based cutoffs had higher prevalence rates in most sex, age, and race/ethnicity groups than the BMI-based cutoffs. Furthermore, the absolute BF% cutoffs overly labeled Hispanic and Other race/ethnicity females with obesity. In summary, childhood obesity prevalence varied by sex, age, race/ethnicity across different cutoffs, with the BMI-based cutoffs showing closer alignments than the BF%-based cutoffs.