You know, D? Sandi just made a really valid point I overlooked. Kids have the unique ability to decide anything going wrong must somehow be their fault.
You do need to speak with W about what to tell them to avoid this. My suggestion? Write out your thoughts/ideas before calling. Stay to your script as much as you can. Put aside your irritation with W, and focus on the kids. Businesslike, mildly friendly...think "neighbor".