How do you make these symbols disappear?

These symbols appeared on my child's iPad many months ago (unsure what app was in use at the time). I They appear on lock screen, home screen and ANY app that is open so are always in the way. The symbol rotates with the screen so always in the top RH corner. (You can't move them or click on them).

I have done a hard-restart after the 4 symbols appeared. They all disappeared but a day later the arrow symbol appeared. And now has changed again. Any ideas of how to get rid of them without resetting to factory settings?