Since Flora was working on the pie crust, and her hands weren't gooey yet, or wet, or covered in turkey, she was the one who got Sora the cereal box, the bowl, and the milk, along with a spoon. He could help himself to how much he wanted.
"That's lovely, dear," Fauna said with a smile. "Do you want to peel potatoes? Riku usually helps us with the bread... that's kind of his thing now, but I'm sure you can help him when he gets to it. But you can't have Christmas Dinner without potatoes, and we have lots of them."