Yes, the matter of 'losing' a session is troubling. For myself, routine is part of the therapeutic experience. I have a psychiatrist that has made mistakes using the appointment scheduler on his computer. I thus confirm with the administrative staff in his office the date and time. I never leave the office without an appointment for the next.

You are very good in that you are acknowledging your youngest's feelings and validate them as being his own.

I have a question about this sort of therapy as it is a new idea to me. How involved are you in the actual therapy? Does the therapist give you instructions for between sessions? Would it be appropriate to ask her to do so?