On iOS devices, we have a special integration with Apple that allows us to remove most apps from the device for some period of time. When we issue another command, apps reappear instantly. Don't worry we are not actually removing the apps so this feels pretty instantaneous. All app data and logins are preserved. Your kid does not have to download apps again.
On Android, we have the ability to display our screen on top of other apps and we do that at the appropriate times to prevent your kid from using other apps.