The backstory is that all of our daughters' friends called us Mom and Dad. Our house was where they all gathered. We didn't mind -- that way, we knew where our kids were and what they were doing!
A few years ago, my niece's next door neighbor became very sick one night, and called her for help. My niece and sister decided that the best way to handle it was for my niece to keep the children at her home, while my sister drove the neighbor to the hospital.
In the ER, the nurse asked the neighbor if she wanted her to get anyone from the waiting room to sit with her while she was waiting in the treatment cubicle, and if so, what name should the nurse call for. The neighbor was immensely embarrassed to admit that she had no idea what my sister's name was...she only knew her as Nana.