Nobody likes making the phone call that a child needs to be picked up early due to severe behavior, or worse, that a family is being counseled out of your program. When delivering bad news to a parent, your delivery and tone dictate the entire direction of the conversation. If you sound hesitant or defensive, the parent will immediately push back.
Start with empathy, but get straight to the point within the first three sentences. Parents appreciate direct transparency much more than they appreciate someone beating around the bush. Use objective facts instead of subjective feelings. Do not say, "He was acting out and being mean today." Say, "He threw three wooden blocks at his classmates during circle time." Have all of your incident reports and behavioral logs printed and sitting on the desk before they arrive. When you present documented, timestamped evidence calmly and professionally, most parents shift from defensive to cooperative almost immediately.