Prep the pan: Preheat the oven to 350°F (175°C). Line a 12-cup muffin pan with paper liners or grease well.
For toddlers, mini muffins are great—use a mini pan and reduce the bake time.
Soften the oats: In a bowl, combine 1 cup rolled oats with 3/4 cup milk. Let sit 10 minutes to soften. This gives the muffins a tender, moist texture.
Mix 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 a small pinch of salt.
Whisk wet ingredients: In a large bowl, whisk 1/2 cup unsweetened applesauce, 1 large egg, 1/4 cup maple syrup, 1/4 cup oil or melted butter, and 1 teaspoon vanilla.
Add apple and oats: Stir in 1 medium grated apple (excess liquid lightly squeezed out if very juicy) and the softened oat mixture until combined.
Combine: Add the dry ingredients to the wet and fold gently just until no dry streaks remain.
The batter will be thick. If using add-ins, fold in 1/4 cup finely chopped raisins or tiny diced apple.
Portion: Divide the batter evenly among the muffin cups, filling about 3/4 full. Sprinkle a few oats on top if you like.
Bake: Bake regular muffins for 16–20 minutes, or mini muffins for 10–13 minutes, until a toothpick comes out clean or the tops spring back when touched.
Cool: Let cool in the pan for 5 minutes, then transfer to a rack.
Cool completely for toddlers to avoid burns and to help the muffins set.