Please ask the parents to go to their App store> click on their profile (top right), go to Apps, find the ParentMail App, click update
Note: do not search parentmail in the search tab.
google play store for android is similar - go to play store, click profile (top right), manage app and device, updates available, locate the app, click update
If its not working, Please ask the parent to uninstall the app and reinstall it.