Preheat oven to 175 degrees C. Line a baking tray with baking paper.
Beat butter, brown sugar and caster sugar together in a bowl until fluffy. Add egg and vanilla extract; mix until combined.
Whisk flour, bi carb and salt together in a bowl; add to butter mixture until dough is just mixed. Fold in infant cereal, oats and quinoa. Drop dough by teaspoonfuls onto baking tary, approximately 5cm apart.
Bake in the preheated oven until edges are golden, 10 to 15 minutes. Let cool on baking tray for 5 minutes; transfer to a wire rack to cool completely.
You can freeze these cookies unbaked, and then bake from frozen as many as you'd like. Use a small ice cream scoop to drop cookies onto a baking paper-lined baking tray. Place in freezer for a couple of hours until firm.