@BrookeKest I am incredibly sorry about the egregious influx of notifications you are receiving. I hope you don't get discouraged about your role as an Observer for your students. I looked into the notifications that you are receiving, and the issue lies with an external tool that is embedded in at least one of the students courses. This external site is posting grades in Canvas for numerous assignments at least every hour--even if there is no change to the grades for you student. Every time the grades get posted to Canvas unfortunately, a new notification is sent to you about the assignment being graded. You can manage the notifications from one course following the process here How do I manage notifications for a single course as an observer?
The admin at the school or the teacher of the course will need to correct the configuration on this external tool for it to stop sending grades to Canvas this frequently, but in the meantime, instead of disabling all Canvas notifications, I would recommend that you change the notifications for the course in question so that either you don't receive notifications about assignments getting graded for that particular course, or change the frequency for that course to being a Daily digest. This will allow you to receive a managable number of notifications from Canvas and allow you to keep up to date about your children.
In regards to the notifications you received after you disabled notification, changes to notifications (especially email notifications) do not take effect immediately and can take a few hours to completely register in the system (and for queued messages to be sent out).