It's not likely to hurt them. They usually like the feel and will toss and play with it, but rare if they eat it. However, they could get some of the banana on their claws, thus licking their paws and cleaning their claws. If anything they would purge this up on their own just like a hairball.
my cat used to eat small amounts of coconut oil, he loved the stuff so much hed get excited every time he heard the tub just like he would with fish etc and he never got sick or any reaction
i dont see why eating bananas would be bad for them, and as for playing with them, its unlikely theres anything bad going to come out of that. theyll probably be fascinated with the texture!