Elementary is the only school setting I have not worked in - I've been a school nurse in early childhood, where there is usually a classroom aide who did this, and in middle and high school, where I did not see this.
Perhaps it is (do you?) because you have a private bathroom?
how often does this happen?
Is it the same kids all the time?
What is the bathroom schedule for the class?
Do the restrooms provide privacy? One nurse I know was caught up in a cycle like this and found out they had taken off all the doors to the stalls to PREVENT GRAFFITTI!!!!! Half the kids were having accidents, the other half were having urinary tract infections and or constipation - she got the doors put back on.
Are the rest rooms clean? Stocked with toilet paper? safe? Scary? Are the kidnergarteners sent the same time as 4th 5th or 6th graders? In Minneapolis a kindergarten boy was sexually assualted by four 4th graders in the restroom during school hours.
Can you work with the teacher on a way to prevent the accidents? I can tell you right now, decades later, who in my own elementary class ever had an accident in school - it's humiliating, so effort should go into the prevention.
Other nurses I know ask the child to clean themselves up, no matter what age, in the closed nurse's office bathroom. They are given wipeups, towels, soap, etc. If there is no clean clothes, the parents are called.
I heard on the radio that this fall there was an influx of children in kindergartens that were not toilet trained. These are NOT special education kids or children with any special health condition. Has anyone seen this? I wonder if toilet training is taking place so late that it is not complete prior to the start of school? The average age when fully trained has gone up considerably in the last 20 years, with the majority of children being fully trained well over 3 years of age.
Bakker, E. & Wyndaele, J. J. (2002). Changes in toilet training in the last 60 years: The cause of an increase in lower urinary dysfunction? BJU International, 86, 248 - 252.
Brazelton, T. B., Christophersen, E. R., Frauman, A. C., Gorski, P. A., Poole, J. M., Stadtler, A. C., 7 Wright, C. (1999). Instruction, timeliness, and medical influences affecting toilet training. Pediatrics, 103, 1353 - 1358.