From the Super Mario Wiki
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Sunflower Kids, also known as Kid Sunflowers and Sunflowers, are a kind of flower found on Isle Delfino in Super Mario Sunshine. They live outside of Pinna Park. At one point, the Snooza Koopas start nibbling on their roots, causing them to turn brown and start to wilt. Mario has to destroy each Snooza Koopa to turn each Sunflower Kid back to its original healthy state. There is also a giant sunflower called the Great Sunflower, who gives Mario a Shine Sprite after every Sunflower Kid has been restored.
Several Sunflower Kids make a small appearance in Mario Kart: Double Dash!!, where they can be seen happily dancing in Peach Beach during the Award Ceremony after players beat a racing cup. Other sunflowers appear in the game; however, they don't look much like the Sunflower Kids, although they do have eyes, just like the kids.