Hi & welcome to Silkysteps.
Umm what about Banana Boomerangs ??
Smoothies sound like a great idea, and for those not keen on bananas other fruits like Strawberrries, raspberries, grapes, tinned fruit - peaches, tangerines etc could be on offer.
If the children can make up their own individual smoothies you could let them choose and chop up 3 different pieces of fruit and then drop it into their own cup until ready to blitz !!
The boomerang bit could be the 'labels that the children can put thier name on / colour in and then attach to a chunky straw with a small double sided foam sticky pad - add the straw to the finished smoothie ..
The label & straw could always be pre made at home or planned for separately if it's easier to have the sole focus of the activity on the fruit & method ..
Hth
Enjoy yourself here