Red White and Blueberry Sundae

watermelon (, your choice of size)

carton vanilla ice cream ((quart size or larger))

carton strawberry ice cream ((quart size or larger))

carton blueberry ice cream or frozen yogurt ((pint size or larger))

jar marshmallow sauce

whipped cream

red (, white and blue sprinkles, divided use)

white candy melts

whole strawberries

For the strawberry sauce:

fresh strawberries (, finely diced)

sugar

vanilla extract

juice from 1/2 lemon

cornstarch

For the blueberry sauce:

fresh blueberries

sugar

vanilla extract

cornstarch