Ds is 11 and is HF ASD with ADHD. He was chatting with his 4 year old sister, and she fell over and landed on his chest, he was lying on the
floor. He then pushed her off and she ran off crying. I didn't see properly what happened and told him he must be careful with his sister because she is 7 years younger than him, and could get hurt more easily. He understands what I am saying but obviously took it to mean "You hurt your sister on purpose and are a bad and terrible boy" I apologised afterwards, and tried to explain but it was too late. He spent the evening in tears, and I ruined his day 
Sorry I don't expect any replies just feeling awful and stressed about it. He relies on me to understand him, to help him with his anxieties, and now look what I did! 