To make the yellow "base," combine the water, mango, banana, and honey (if using) in a blender and blend until completely smooth. If you want to make the popsicle pictured above, with the yellow layer in the middle, pour about 2/3 of the mixture into a separate cup and set it aside. Note: If you don't have a super-picky toddler, I personally would just use the yellow smoothie as the "top" of your popsicle and add the next colored layers after that. My son wanted the yellow part to be in the middle, so that's why I'm making the top layer now, in the second step, instead of in the first step. Hopefully that's not too confusing. Feel free to switch these layers around if you'd prefer!
To the remaining smoothie that is left in the blender (there should be about 1 cup of yellow smoothie left in there) add in a small handful of fresh baby spinach. Blend until the spinach is completely broken down, then pour the greens smoothie into the bottom of each popsicle mold. Fill the popsicle mold only 1/3 of the way up, to leave room for more layers later. Place the popsicle mold with the green smoothie filling in the freezer to set for 20 minutes. Set a timer, so you don't forget! I also like to place the yellow filling that you set aside in the fridge or freezer, so it stays nice and cold. If you let it get too liquid-y at room temperature, it will be difficult to layer in the popsicle molds later. (Colder filling works best!)
When the timer goes off, simply pour the yellow mixture on top of the frozen green layer, leaving some space at the top of the mold for the third layer. The yellow should sit right on top of the green. If for some reason it breaks through the green layer, it means the yellow is too runny or the first layer isn't firm enough yet. In that case, return the popsicles and yellow filling to the freezer to firm-up some more, about 15 more minutes. Once you've added the second layer, return the popsicles to the freezer for another 20 minutes. Set a timer!
To make the final layer, add your remaining yellow smoothie back into the blender, and add in 4 to 5 frozen strawberries. Blend until very smooth, adding a splash of water if needed to help facilitate blending. Remove the popsicle molds from the freezer, and add the last layer, filling the molds only to the "fill line." You want to leave some space at the top to account for frozen things expanding.
Insert a stick into each mold, making sure it goes through all three layers, and then return the popsicles to the freezer to freeze until solid, 4 to 6 hours.
To remove the popsicles from the molds, simply run each one under warm water for about 30 to 60 seconds. The sleeve should pop right off! (That's why I like this particular mold set-- each popsicle is individual, so you can easily thaw one at a time.)