Thank you for writing.

There are many insect pests that eat sunflower leaves. https://extension.umn.edu/flowers/sunflowers

Grasshoppers are possible along with many other insects.

Your damage is very mild but could accelerate. The problem is this. Sunflowers attract many pollinators and any insecticide will be detrimental to highly beneficial insects that are becoming much less common. Considering the large size of grasshoppers, you might try insect barrier mesh which lets sun and water through. You probably could leave the flowers exposed.  THere are many brands that are widely available at major garden centers.