In a large bowl, dissolve yeast in water that is between 105 and 115 degrees.
Add the sugar, salt, and 3 cups flour. Beat by hand until smooth. Stir in enough remaining flour, 1/2 cup at a time, to form a soft dough.
Turn onto a floured surface; knead until smooth and elastic, about 8-10 minutes. Place in a greased bowl, turning once to grease the top. (You can also do this in a stand mixer with dough attachment)
Cover and let rise in a warm place until doubled, about 1-1/2 hours.
Punch dough down. Turn onto a lightly floured surface; divide dough in half. Shape each into a loaf.
Place in two greased 9x5-in. loaf pans. Brush top with warm water and sprinkle rainbow sprinkles over top.
Place bowl in a warm dry place (uncovered) and let rise until doubled, about 30-45 minutes.
Bake loaves at 375° for 30-35 minutes or until golden brown and bread sounds hollow when tapped.
Remove from pans to wire racks to cool.