In a mixing bowl, whisk together the flour, sugar, baking powder, and salt.
In another bowl, beat the egg and add the milk, melted butter, and vanilla extract. Mix well.
Pour the wet ingredients into the dry ingredients and stir until just combined. Don't overmix; a few lumps are okay.
Gently fold in the rainbow sprinkles into the pancake batter.
Preheat a griddle or non-stick skillet over medium heat and lightly grease it with butter or cooking spray.
Using a ¼ cup measuring cup, pour the pancake batter onto the hot griddle to form pancakes.
Cook until you see bubbles forming on the surface of the pancakes, about 2-3 minutes.