Video calls (VOIP calls)
Safe Lagoon can effectively block the on-screen content for video calls. However, we can't block the actual calls (i.e. the audio stream and the call notifications on modern Android versions).
If a child presses the OK button on the blocking screen or taps the Back button, the behavior may differ on different versions of Android:
for Android 7 and below the system will close the activity
for Android 8+ the system may minimize the messenger's activity and show it in a picture-in-picture view. It depends on whether a messenger supports such a mode or not
Major messengers do support this mode (for instance, WhatsApp and Viber). Luckily, parents can disable the mode in the system settings. They need to open Settings -> Apps -> App info -> look for Picture-in-picture and disable it. This doesn't stop the call, but children won't be able to see their dialog partner anymore.
Chat heads (bubbles)
Normally, Safe Lagoon tracks push notifications for the blocked apps and hides them if there is some blocking rule in place. Therefore, children shouldn't be able to reply in the notifications area because there are no visible notifications.
However, there is at least one known exception. Facebook Messenger has a unique feature that's called Heads (Chat Heads). It is an overlay view and looks like a circle with an avatar image in it. The feature is enabled by default and can't be blocked because it's an overlay. Nevertheless, parents can disable the feature in the messenger's settings and kids won't be able to use it.
Recently the same feature was released in Android 11 and almost fully copies Facebook's implementation but for all messengers and with the same consequences for us. Fortunately, parents can disable the feature in Settings -> Apps & notifications -> Notifications -> Bubbles -> Disallow all apps to show bubbles.
A similar feature exists on modern Samsung devices and it’s called Smart pop-up view. Parents can disable the feature in the system settings as well.