With your thumbnail make a gash in the top inside of the banana right below the stem. Do this surreptitiously when you’re kids aren’t looking.
Then hold the banana upside down by the stem with the gash side facing you.
Say, “I AM MORE MAGICAL THAN THE AMAZING RANDY. I AM MORE DARING THAN EVEL KNIEVEL. I CAN OPEN THIS BANANA USING MY MAGICAL POWERS. ARE YOU READY?”
(Since kids will figure out the trick pretty quickly, you’ve got to milk it for all it’s worth the first time you do it.)
Flick your wrist so you are flicking the banana down and away from you. PRESTO-ALA-KAZAM, the banana peel will give way on the gash you made and you’ll be holding an open banana by a piece of peel.