My 6 year old(middle child) makes comments a out everyone hates him and I should kill him with a knife, and it scares me.

I'm wondering if I should have him speak with someone. We had a meeting with his school and they don't see this type of behavior at all, so we assume it must be something at home. Our other 2 children don't have this issue at all, the self depreciating and suicide/murder talk. Very basic things will set him off, but then he'll be the kindest angel. We were worried he had aspergers of some sort, but the school thinks he has ADHD. I'm concerned it's chemical and he might hurt himself when he is older for attention. Has anyone had a child like this, what did you do?Thank you. via /r/Parenting https://ift.tt/2SsQm8k