So the way notifications work is, if a parent has the app installed on a device and its open and they have allowed notifications in their device settings, they will get push notifications when their child is tagged in a post, if those push notifications do not get answered (i.e. they do not open the app) they will also get an email at 4pm notifying them of updates.
Of course if they logon at any time and see the post/s this renders both the push and email inactive as they have seen the post )