Preheat oven to 400°F. Line 12 muffin tins with liners and set aside.

Prepare crumb topping: In a medium bowl, combine flour and sugar. Cut in butter until mixture forms crumbs. Set aside.

In a medium bowl, mix flour, baking soda, salt, and sprinkles. In a large bowl, whisk together the sugar, vanilla, buttermilk, oil, and eggs. Add dry mixture to the wet mixture and fold with a wooden spoon until just barely blended.

Fill muffin tins 3/4 full. Divide crumb topping evenly among muffins, sprinkling generously on the top. Bake for about 15 minutes, until a toothpick inserted in the center of the muffins comes out clean. Let muffins cool in pan for about 20-30 minutes. Remove to wire rack.

In a medium bowl, whisk together powdered sugar and water. Drizzle over muffins.