Prep the pan: Preheat your oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper, leaving a little overhang for easy lifting.
Mash bananas: In a large bowl, mash the bananas with a fork until smooth with small lumps.
Add wet ingredients: Stir in the egg (or flax egg), applesauce or yogurt, melted butter or coconut oil, and vanilla until well combined.
Mix dry ingredients: Add oats, cinnamon, baking powder, and salt.
Stir until the oats are evenly coated and the mixture looks thick and spoonable.
Fold in extras: If using chia, hemp, soft berries, or finely chopped nuts, fold them in gently.
Spread and level: Pour the batter into the prepared pan and smooth the top with a spatula so it bakes evenly.
Bake: Bake for 22–28 minutes, until the top is set and lightly golden around the edges. A toothpick inserted in the center should come out mostly clean.
Cool completely: Let the bars cool in the pan for at least 20–30 minutes. Lift out with the parchment and cut into small squares or bars sized for your child.
Serve: Offer as-is or with a swipe of nut butter, cream cheese, or a dollop of yogurt.