Add the watermelon cubes to a blender and blend until smooth and liquid.
Pour the watermelon juice into popsicle molds, filling each mold about three-fourths full. Leave a little space at the top for the yogurt and kiwi layers.
Insert popsicle sticks and freeze for about 2 hours, or until the watermelon layer is partly firm.
Mix the yogurt with honey or maple syrup, if using.
Remove the molds from the freezer and spoon a small layer of yogurt over the watermelon layer.
Freeze again for about 45 minutes, or until the yogurt layer is slightly firm.
Blend the kiwi until smooth, adding a little honey or maple syrup if you want it sweeter.
Pour the kiwi puree over the yogurt layer.
Freeze for 4 hours, or until completely firm.
To unmold, run the outside of the molds under warm water for a few seconds, then gently pull out the popsicles.
