Bright green cupcakes with buttercream that tastes like watermelon! Add mini chocolate chips for the watermelon seeds! It could be nice to do the reverse red velvet cake w/ chocolate chips and green frosting.
Add a fruit, a juice box, No GMO chip bag, and a sub sandwich. Place large blankets down on the grass and have a group picnic. Food served in beach-pail. this would so cool if your kid had a birthday at the beach--indoor beach party?