Ice cream parlour... about 5 different flavours, sauces, sprinkles, choc flakes and matchmakers to stick in cones and plastic sundae dishes and those little sparklers you get for cakes etc. regularly do this for barbecue parties also with some syrups and icecream thick milkshakes
You can also get a fountain for your non alcoholic cocktail just need to keep topping it up,, also keep checking any fruit punch for illegal additions even at thirteen there is a good chance that some parents drinks cabinet will be raided