The boy was to young to know what he was doing this was exploration if you really want to prove it to your family ask a phsyciatrist if most eleven year olds knew about sex at the time.
I forgot to add this, because often after I post the original poster adds a comment that changes the whole story so my response is inappropriate.
If this is exactly as you are telling it, and your son hasn't done things all along so that this experimentation was merely the straw that broke the camel's back, the above post stands.
Best wishes.
annemarie, our society has lost our minds where child sex play is concerned. Had he pushed her down a flight of stairs three times, rather than looking at her genitals, your family would probably not have disowned you.
An 11 year old, and a 7 year old, are pretty contemporary. This isn't like a 17 year old boy and a 2 year old girl. Both kids knew what they were doing and did this willingly.
If your family has disowned you for this, you've suffered no great loss. Fill your lives with good friends and people you love and enjoy, and let them go. They weren't worth it to begin with, and they never were all that attached to you at all if this is all it takes (after two years of no one seeming harmed) to dismiss your family.
Best wishes. Reading these boards this happens a LOT. Support your son, and get on with your life.