It may seem very simple, but it's actually crucial for kids (especially picky eaters) to manipulate the fruits and vegetables they eat. I guarantee that kids are more likely to try fruits and vegetables that they've had a chance to slice, or cube (or cut into any shape they wish). My 10-year-old uses my paring and chef's knife because he is able to responsibly use them, but my 7-year-old uses Curious Chef plastic knives that I ordered from Amazon.
Also have kids use cookie-cutters to cut their own fruit.
However, please eat the remaining piece to avoid food waste!