Oh, I am so sorry. I'd write a letter to my friend, expressing my grief and concern and thanking her for our continued friendship.
Aslo...
Because of some of the other answers below, I looked back to see what they were talking about. I have a 7 year old and we are in the process of having him evaluated for ADHD. He also has difficulty being still - ever. He also sometimes displays actions that are really not appropriate to the setting. But he would not throw an animal around. I'd say any need to watch for that kind of thing happening -due to undeveloped reasoning- ended between age 3 and 4.
With ADD/ADHD, we already know something is amiss in our child's brain. We know early intervention helps and can mean a perfectly normal life.
If your child is bright, you probably alreay suspect more. I have read (I don't have data) that there are many more sociopaths that we realize - because most of them *never* do anything violent. They are instead taught right and wrong as children and manage to process that teaching - even if they never feel any guilt. Please understand that if you suspect such a thing, they very best thing you can do is get help. The potential for a child to grow up and be nice and at least intellectually "empathetic" is real.
If your child has mental challenges, then you know you have a different path. I know from my own childhood playmates that children with specific mental challenges can become violent when they mean to be affectionate. No ill is meant, no empathy is missing. Capacity to reason and process cause and effect just isn't available.
So...I didn't read enough to have any *idea* what might be going on. And I wouldn't be qualified to guess either. But if you have behavioral therapy going for the ADD, wouldn't this be worthy of dicussion?
I wish you the best. My heart is aching for you.
I hope you don't mind these additional thoughts. I know hearing such things isn'te asy. And anyway, we could all be very wrong. Only you can know.
best to you,
e