Update:
My supervisor attended the next session and had a meeting with the mom. If I don't want to work with that family anymore my supervisor will work with me, (but I feel like I don't want to abandon my client, so I'm going to continue working at that home), and it's understood that I'll call the police if it happens again.
I had a T appointment and we talked about it a great deal. I/we feel better about the situation. There are so many things we can do now that we couldn't do years ago. The last session at that house went very well, no weirdness (and that little kid was so happy to see me) so that helps too.
After I got home on the night of all that craziness, though, I actually lost time. That is very rare for us, especially these days. I still can't remember going to bed.