Jim,
I am so sad to read what you wrote, but it's an accurate rendering of how children were seen and treated at that time and how people saw the Church and priests.  I'm sorry that your mother failed you, but I'm not sure that she could have done anything else.  I remember all too well how women and girls were treated at that time.  If she had pushed the issue, she would have been written off as a hysterical mother.  Perhaps she did believe you at some level, but it may have been just too much to cope with.  I can't imagine having 7 children, the youngest a few months old, and my son coming to me with a story like that, back in the early 60s .....
But I am soooooo angry about the institution and the individuals that enabled this to happen.  
I am glad that you have survived and can tell everyone the truth.  Congratulations on that.  It's not an easy journey.