Dogs aren’t much different than people when it comes to getting in trouble. They don’t want to take the blame for something they didn’t do. Especially, if it’s a brother and sister duo. Just think of all the times your brother or sister tried to blame you when it wasn’t your fault. Or maybe it was the other way around.
When these two get caught by their dad, it’s obvious who was the one who was up to no good. Charlie doesn’t hesitate to let dad know who committed the crime.