Prep the oven and pan. Heat the oven to 350°F (175°C). Lightly grease a 12-cup muffin tin or line with paper liners. For very young toddlers, you can use a mini muffin pan and reduce baking time.
Soften the oats. In a bowl, combine 1 cup rolled oats with 1 cup milk.
Let them sit 10 minutes to hydrate. This is key for a soft, moist texture.
Mix the wet ingredients. Whisk 1 cup pumpkin puree, 2 eggs, 1/4 cup unsweetened applesauce, 1/4 cup maple syrup (or to taste), 2 tablespoons oil or melted butter, and 1 teaspoon vanilla. Stir in the soaked oats and milk.
Combine the dry ingredients. In a separate bowl, whisk 1 cup whole wheat flour, 1 1/2 teaspoons baking powder, 1/2 teaspoon baking soda, 1 teaspoon cinnamon, a pinch of nutmeg (optional), and 1/4 teaspoon salt.
Bring it together. Add the dry mixture to the wet mixture.
Stir gently until just combined. The batter should be thick but scoopable. Fold in 1/4–1/3 cup of optional add-ins if using.
Portion and bake. Fill each muffin cup almost to the top for full, rounded muffins.
Bake standard muffins 16–20 minutes, or mini muffins 10–13 minutes, until a toothpick comes out clean or with a few moist crumbs.
Cool before serving. Let muffins cool in the pan 5 minutes, then move to a rack. Serve slightly warm or at room temperature. For toddlers, slice in half if needed.