Pumping Cover Story

So during a normal school year, I'd just drop my students off at the cafeteria for lunch, pump, then pick them back up, and my teammates would cover for me. The students wouldn't notice I was gone. This year due to COVID, we're eating in the classroom, so my teammate has to stand in the hall and monitor both classes. It's really obvious that I'm missing. Does anyone have any suggestions for a good cover story? I don't particularly want to explain pumping to a bunch of 6th graders.