AS AnAmericanMother, I figured you would crack up at what I said.
Every real American mom has had such an experience.
Elementary school violin students' concert. About 15 students.
The accompanist didn't show up.
I was accompanying my daughter already, so the teacher asked, "Would you mind . . . . . "
Got some good sightreading practice in, and fortunately all the kids were at a pretty basic level so none of the music was too hard. And some of the stuff I even knew already (Bach's Minuet in G - if I ever hear that again. . . !)
The most interesting thing I learned was when a kid stumbled or got lost how to wait for them (and throw an encouraging smile to them in the meantime).