What is this on my iPad screen & how do I get rid of it?

My iPad mini never used to have this on it. I let my young kid play with it one day & after he was done with it, it was there. It's real annoying & id like to get rid of it. It's a white/clearish square with a dot in the center of it that when clicked opens some type controls. It's real annoying & if you know how to get rid of it let me know.

Please take a look at the photo. Top left corner.

Thank you



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