Most iOS devices will use about 1gb of data per month. Some might be a little bit higher based on drivers, but the pool should average out to around 1 gb per month.
If you are finding that number to be higher, here are some things you can try:
- Make sure devices have regular access to wifi
- Make sure Settings - iTunes and App Stores - Automatic Downloads - Updates is ON
- Make sure Settings - iTunes and App Stores - Use Cellular Data is OFF
- Make sure Settings - Cellular - WiFi Assist is OFF
- Check the apps toggled ON under Settings - Cellular - Cellular Data are ones that you want on
- Enable Content & Privacy Restrictions and turn off access to Apps like Safari, Social Media and other apps that drivers should not be using. For ParaPlan, drivers only need access to ParaPlan, Google Maps, Apple Maps and Phone