Preheat the oven to 350°F. Grease and flour two 9-inch round cake pans.

In a large mixing bowl, cream together the softened butter and sugar until light and fluffy. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the butter mixture, alternating with the milk. Mix until just combined.

Divide the batter evenly into three bowls. Leave one bowl plain, add red food coloring to the second bowl, and blue food coloring to the third bowl. Mix until the colors are vibrant.

Pour the batters into the prepared cake pans, alternating colors to create a marbled effect. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean. Allow the cakes to cool in the pans for 10 minutes before transferring to a wire rack to cool completely.

Once the cakes are cool, crumble them into a large bowl. Layer the crumbled cake, whipped cream, sliced strawberries, and blueberries in push pop containers. Start with a layer of red cake, followed by whipped cream, strawberries, blue cake, whipped cream, and blueberries. Repeat until the containers are full.

Chill the push pops in the refrigerator for at least 30 minutes before serving to allow the flavors to meld.