The black boy
I was watching this with a friend of mine, who seemed to automatically assume the black boy would be ostracized or discriminated against. He was surprised to see that the boy was subjected to no racism in the film, he was considered just one of the gang and even given the position of 'district attorney' in their little justice system. None of the guards even seem to care.
I just thought his reaction was interesting and probably pretty common, everyone seems to think that back then a black kid MUST HAVE been given a hard time on a daily basis, but people haven't really changed as much as everyone seems to believe.
Just a minor thing I thought I'd point out. I'm a huge fan of early cinema and especially love '30s gangster-fare, but it seems like everyone I watch these kinds of films with always holds some kind of skewed misperception about the past. 'Mayor of Hell' was pretty good, though far from Cagney's best. Didn't think the plot was terribly engaging in this one. My first thought was 'I wonder how the Dead End Kids would've handled this script!', then I found out they were in Crime School (1938), essentially a remake of this film, which doesn't seem to have garnered too much critical acclaim.