Prep the pan: Heat the oven to 350°F (175°C). Line an 8x8-inch pan with parchment, letting the edges overhang for easy lifting.
Mash the bananas: In a large bowl, mash 3 ripe bananas until smooth with a few small lumps.
You should have about 1 to 1 1/4 cups.
Whisk the wet ingredients: Add 1/3 cup unsweetened applesauce, 1 egg (or flax egg: 1 tablespoon ground flax + 3 tablespoons water, rested 5 minutes), 1/3 cup milk, 1 teaspoon vanilla, and mix until combined.
Stir in the dry ingredients: Add 1 1/2 cups rolled oats, 1/2 cup oat flour, 1 tablespoon chia seeds, 1 teaspoon baking powder, 1 teaspoon cinnamon, and a small pinch of salt. Stir until everything is evenly moistened. The batter will be thick.
Fold in extras (optional): Mix in 1/4 to 1/2 cup of any soft add-ins, like finely diced berries or grated carrot.
Keep pieces small for safer bites.
Spread and smooth: Scoop the batter into the lined pan and smooth the top with a spatula. Press it into the corners so it bakes evenly.
Bake: Bake for 22–28 minutes, until the center feels set and the edges lightly pull away from the sides. A toothpick should come out with moist crumbs but not wet batter.
Cool completely: Let the pan cool on a rack for at least 30 minutes.
Lift out using the parchment and slice into bars or small squares sized for your child’s age.
Serve smart: For younger toddlers, cut into soft sticks for easier grip. For older kids, standard bars work well for lunchboxes.