The African-American reference was included so that one may consider race in assessing whether the child received the appropriate punishment-----Since juries are typically biased against African-Americans. If it had been a caucasion child, race would not have been relevant since very likely the jury and judge would not have been biased.
Here, it looks like race was likely not a controlling factor since the punishment, although still more than I would have given, is reasonable in light of the alternative punishment.