bystander behavior

Last night my aunt and I were walking to her car after leaving Wal Mart with our sons. As we approached our car a young mother was yelling at her children calling them stupid and treating to slap them. Even after they were seated in their car she continued to belittle them and tell them she didn't care what their father had said. I didn't know how to react in this situation because there are so many social norms against interfering with the way some one parents, especially some one who you are not closely acquainted with. If I were to have said something to the lady it would have been along the lines of "Maybe you don't understand but you are damaging the personalities and ability of thier social function for THE REST OF THEIR LIFE! The way a child feels about their home and primary care giver for the first 5 years of their life determines their personality and many traits that lead to dysfunctionalism." The time I wish a bystander had stepped in was also the same day. While in the check out line of the store, I was loading the groceries onto the conveyor belt while my son was busy chewing the corner of a carboard box of cereal. I felt so terrible that I hadn't caught it, not that it went on very long. By the time it was all said and done the lady behind me in line who had witnesses this was starting at me in disgust and I felt TERRIBLE! My toddler is teething and I was trying to get out of line so fast because I hate when people have to wait on me. If only the lady witnessing my child chewing the cereal box had spoken up at first maybe she wouldn't have had such a terrible look on her face. Maybe its just me but I always look after others children and I'm the first to step in, a lot of it probably has to do with the fact that I care about people. I think colege students dpn't speak up against wrong doing because a lot of times they are influenced by peer pressure, constricted by time, unsure how to approach the situation, unclear on their own stance in regards to that situation, and there are so many gray areas.