While I can’t say that it’s impossible for a child to uninstall Qustodio, it would be very difficult to do, and the parent will receive an alert right away. There are several uninstallation protection features that are enabled during installation, such as:
Requiring a username and password to disable or remove the app
Device admin permissions that block any attempt to uninstall the app
Locking device settings to prevent Qustodio from monitoring the device
Hide the app, which is an option on Windows and Macs