I would say yes, you can sell cookies. The only legal issue is allergies. Kids and adults both are developing allergies more recently than anytime in the past, so if you do make cookies, make sure to post the allergens in your ingredients and consider also making vegan-style cookies. Post signs at your stand that say, 'Food contains: milk, egg, nut,' etc. Then, you could also try making cookies that don't have these ingredients, such as egg-white cookies, milkless stove-top cookies, and more. Look around online for good recipes, and good luck with your stand!