Lightly coat three 8-inch square pans and one 9 × 13-inch baking pan with cooking spray.
In three separate bowls, mix each package of flavored gelatin with 2 cups boiling water. Pour each into its own greased square pan. Refrigerate for 2-3 hours.
After the jellos have been in the fridge for a couple of hours, make the milk gelatin. In a 3-quart saucepan, mix the gelatin into 1 cup water.
Set aside for about 5 minutes so the gelatin can bloom.
Set the saucepan over medium-low heat and stir occasionally until the gelatin has dissolved. Add the whole milk and heat to just under a simmer. Add the cinnamon stick, remove from the heat, and let the mixture steep for 30 minutes.
Remove the cinnamon stick and whisk in the condensed milk, half-and- half, and vanilla extract. Set aside while you prep the colored gelatins.
Remove the colored gelatins from the refrigerator and cut each flavor into 1-inch cubes. Evenly spread out and mix each flavor in a 9 × 13-inch pan. A Pyrex casserole pan works great for this.
Pour the cooled milk gelatin over the cubes of already set up Jell-o's. Refrigerate for at least 3 hours, or over-night is even better for this step.
Using a very sharp knife, cut the gelatina con tres leches into cubes and serve in large serving bowl.