Wash and prepare the strawberries by hulling and cutting them in half.
Cut the watermelon into cubes, making sure to remove any seeds if necessary.
Place the strawberries, watermelon, lime juice, honey or agave syrup (if using), and ice cubes (if desired) into the blender.
Blend the mixture on high speed until smooth, ensuring there are no chunks remaining.
If the mixture is too thick, you can add a little water to help thin it out.
Taste the slush and adjust sweetness if needed by adding more honey or agave, then blend again briefly to combine.
Pour the slush into glasses and serve immediately. Garnish with a slice of watermelon or strawberry on the rim for a decorative touch, if desired.
For an adult version, consider adding a splash of rum or vodka to each serving.
This slush can be stored in the freezer for up to an hour before serving, but for best results, enjoy it fresh.