Rant - You Have To Be Carefully Taught

I am really mad and if anyone thinks I did the wrong thing I don't want to hear it! I am from Guadalajara and my two charges,little girls 8 and 6 are African-American. At the playground 3 days ago a boy, about 6, used a very inappropriate word which starts with N. He was up on the slide and when my 2 charges ran over giggling  to climb up the slide he looked at them with an angry look and said what he said.I had heard it and my mouth was open, my 8 year old charge in particular was upset and confused, and wanted to know why he said that. I walked right over to the boy, told him I heard what he said and that it was very hurtful and wrong and I insisted strongly that he apologize to the two girls. He looked very sheepish and whispered "sorry". Then his mother and older brother came over and I told them firmly what happened, the older brother said something like " leave him alone, he can say what he wants" and the mother refused to address the issue of the horrible word he used and said " I will discipline my child, you are not allowed to speak to him." When we got home I told MB what happened and we had a familiar discussion with her girls like - "ignorant people and words do not define you, you can be anything ever you want."What is WRONG with some people?