my Facebook page with a teacher who was looking for help convincing her administration to allow her students to use Google Earth. In the conversation I was asked if Google offers advice or has a template for getting permission from parents to use their services. The answer is yes. The permission slip template can be found here in the G Suite Administrator help pages.
G Suite administrators can enable Google Earth for their domain users. I'm not a school law expert, but it is my understanding that if you have permission for students to use G Suite tools they can use Google Earth if it is enabled for your schools G Suite domain. (Again, I'm not a school law expert and you should consult with your school's attorneys if you are worried about regulations for your specific situation).
Find the G Suite permission slip template here.
You can learn more about G Suite in my online course G Suite for Teachers. And in Teaching History With Technology you can learn how to use Google Earth and Google Maps.