Keep the iPad cover on the device all the time.
Use a safe protective sleeve to store their devices when travelling to and from school. Try not to put the water bottle, charger and the device in the same bag to prevent damages.
Keep water and food away.
Wash hands before using the devices.
Gently scrub the screen with a 70 percent isopropyl alcohol wipe or Clorox Disinfecting Wipes to remove smudges. Details can be found here https://support.apple.com/en-us/HT204172.
Carry the devices carefully. Hold the iPad by the handle.