The mother should have indeed taken her daughter to the toilet at the restaurant/cafeteria. I think this probably happens more often than we think, especially in places such as the movies where the parent does no want to miss any of the movie.
I remember a little while ago there was a video of a girl in her early 20;s that was sun baking on a towel in her swimsuit in a park. She peed herself and then quickly packs up. Anyone have the video or remember the name of it?