A reader in Towson, who found herself in the same situation I've been in a few times -- and that of many other people -- wonders what to do:

I am a disabled person, and as such, I rely on MTA to travel about.
 
At the end of last week, I was on a bus where I observed reprehensible behavior, to which I responded with deep sadness.  I felt so powerless.
 
I noticed a young mother, with a young child (he was perhaps 2, 2 1/2 years old).
They had just gotten on the bus, and were finding their seats.
 
The next thing I heard was a terrible smacking sound; the mother yelled at her child:
"You are not going to tell me where to sit"; and then, when the young boy began to cry, the Mother yelled at him, "Shut Up".
 
I felt so powerless.
 
I felt so terrible that the young boy was the object of his mother's rage.  Could she have stopped before she lashed out at her son? 
 
I know that you have written about scenes such as this that you have witnessed. What can we do as individuals?  What can we do as citizens?  How do we protect the children in our City from being hurt?  How can we protect the Children of Our World?
 
As silly as it sounds (?), maybe there is a pressing need for Parent Education; i.e. a course of instruction that reaches every mother (and father) who become pregnant, who visit their doctor.
Could/would this help?
 
I am a person who grew up in a damaged home.  My parents were both mentally ill, and my brother and I had to make sense of a world that made no sense.  I have spent a lifetime digging out from the rubble of my Mother's self-hatred and my Father's ignorance and neglect.
 
I weep for children who are mistreated like this young child on the bus.
 
So much goes on in this world.  So much.
 
How can we change this world?  I suppose, One Child At a Time.
 
I wished I could have said something to the young, troubled mother.  Did she know how
she was hurting her son?  Would my words have inflamed her more?
 
I weep when I see an innocent child like this being hurt.

Here's what I say: I say speak up when you see this.
Nothing good comes of hitting kids. Parents teach with their words and deeds. When they
slap a child, they teach violence, and the person who does it in public is
doing much more in private.
   Parents think they have a right to beat children - they call it "spanking"
- after they have failed as adults to correct behaviors, or when they are
drunk or high, or when they are tired and angry, or when they just feel like
it. Many adults think it's just fine because they either do it themselves or
because they had the same experience when they were kids. And, in the great
denial that marks human existence, they don't see the
harm in it.
   And let's face it: We're jaded. We're suckers for the belief that human
beings will never change, that we are doomed to living with the cancer of
ignorance and violence.
   The streets and prisons are full of men and women who were abused as
children, but that fact doesn't stop us from abiding the mistreatment of more
children - either at the hands of their relatives or at the hands of a society
that denies them real opportunities and a chance to rise above poverty and
mediocrity.
   In some ways, believing that humans will never change - or that there's
nothing we can do about violence, that it's just in our nature - is
comforting. It means you can live your life and keep your mouth shut. "Mind
your own business!"
   I say that's no way to live.
   Excuse me for rambling and spouting off.
   But I am sick of the cycles - of addictions, violence, stupidity and failure. We can't give up. We have to do what we can do, in our own little corner of the world, while we still have time. We have to speak up.