Can I and my school district be sued for a little accident in a field trip?

I am a high school environmental science teacher. On a recent water quality testing field trip, one of my students suffered a small chemical burn on the tip of her finger from one of the test kit chemicals after not following the written lab procedure. She was treated at the local urgent care and was back in class the next day. At the time of the incident, she was being supervised by another teacher, but it was my class. Now the student and her mother are hinting at a lawsuit.