In a saucepan over medium-high heat, bring orange juice, lemon juice, and brown sugar to a boil. Reduce heat to medium-low and simmer until slightly thickened, about 5 minutes. Remove from heat and stir in vanilla extract. Set aside to cool.
Layer fruit in a large, clear glass bowl in this order: watermelon, cantaloupe, honeydew, strawberries, and blueberries. Pour cooled sauce over the fruit. Cover and refrigerate for 3–4 hours before serving.
Note: Add pineapple, mango, and kiwi for a tropical touch.