Same issue on current generation Galaxy Tab A.
The quick menu solution works great for us but if you would like kids mode icon to return then you can do the following:
Once in kids mode,
1. Tap on the 3 dots in the top right hand corner and go into parental controls and enter pin no.
2. Click onto the 3 dots again and go into settings.
3. Enable option 'Add Samsung kids home icon'.
This will display the icon as it once was prior to the update. Just find the screen it shows up on and move it to you desired screen.
If kids mode has timed out just access parental mode through the parent icon in the top left and follow steps 2 and 3.
My guess is that this should also probably work on any Samsung device that had kids mode and upgraded to Android 9 pie.
Hope this helps.
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