All the injuries they are describing are normal things that happen to kids everyday. He very well could have scratched himself kicking and screaming and having hissy fits. There is absolutely no proof of abuse from what you describe and any good lawyer would advise the parents not to persue it. They sound like parents who don't want to take responsibility for their childs ridiculous and unacceptable behavior. I have learned from doing home daycare that many parents can't parent their child and need a scapegoat which is daycare more often than not. They are threatening you and trying to intimidate you- Don't let them!