Preheat and prep: Heat the oven to 350°F (175°C).
Line a baking sheet with parchment paper to prevent sticking and make cleanup easy.
Mash the bananas: In a large bowl, mash the bananas with a fork until mostly smooth. A few small lumps are fine and add moisture.
Add wet ingredients: Stir in applesauce (or melted coconut oil), vanilla, and cinnamon. Mix until well combined.
Stir in dry ingredients: Add oats, ground flax (or chia), and a pinch of salt if using.
Fold in your chosen add-ins. The dough should be thick and sticky, not runny.
Rest briefly: Let the mixture sit for 5 minutes so the oats and seeds can absorb some moisture. This helps the cookies hold their shape.
Shape the cookies: Scoop heaping tablespoons onto the baking sheet.
Use damp fingers to press each mound into a flat round about 1/2 inch thick. Thinner cookies bake more evenly for toddlers.
Bake: Bake for 12–15 minutes, until the edges feel set and the tops look dry. They won’t brown much, so check texture more than color.
Cool completely: Let the cookies cool on the sheet for 5 minutes, then transfer to a rack.
Cooling helps them firm up and become easier for little hands to hold.