Step 1- Blend the Fruit
Place the watermelon and kiwi in a blender along with any optional variations you're using, like lime juice or mint. Blend until completely smooth.
Step 2- Taste and Adjust
Give the mixture a taste. If your watermelon isn't particularly sweet, add a small drop of agave to balance things out. Ripe, in-season watermelon usually doesn't need any extra sweetener at all.
Step 3- Fill the Molds
Pour the blended fruit mixture into popsicle molds, leaving a little room at the top since the mixture expands slightly as it freezes.
Step 4- Freeze Until Solid
Freeze the popsicles overnight, or for at least 6 hours, until they've hardened all the way through. Rushing this step leaves you with a slushy center instead of a proper solid popsicle.
That's genuinely the entire process. Two active steps, and a lot of patient waiting while your freezer does the real work.