Objective: We compared Child Behavior Checklist (CBCL)-AAA (Attention Problems, Aggressive Behavior, and Anxious/Depressed) and Parent–Young Mania Rating Scale (P-YMRS) profiles in Brazilian children with ADHD, pediatric-onset bipolar disorder (PBD), and PBD + ADHD. Method: Following analyses of variance or Kruskal–Wallis tests with multiple-comparison Least Significant Difference (LSD) or Dunn’s Tests, thresholds were determined by Mann–Whitney U Tests and receiver operating characteristic (ROC) plots. Results: Relative to ADHD, PBD and PBD + ADHD groups scored higher on the Anxious/Depressed, Thought Problems, Rule-Breaking, and Aggressive Behavior subscales and Conduct/Delinquency Diagnostic Scale of the CBCL; all three had similar attention problems. The PBD and PBD + ADHD groups scored higher than the ADHD and healthy control (HC) groups on all CBCL problem scales. The AAA-profile ROC had good diagnostic prediction of PBD + ADHD. PBD and PBD-ADHD were associated with (similarly) elevated P-YMRS scores. Conclusion: The CBCL-PBD and P-YMRS can be used to screen for manic behavior and assist in differential diagnosis.