Prepare the Oven
Preheat oven to 350°F (175°C). Grease and line both the round and square cake pans.Mix the Dry Ingredients
In a bowl, whisk together flour, baking powder, and salt. Set aside.Cream Butter and Sugar
In a large bowl, beat butter and sugar until light and fluffy (about 2 to 3 minutes).Add Eggs and Liquids
Add eggs one at a time, mixing well after each addition. Stir in milk and vanilla extract.Combine Batter
Gradually add dry ingredients to the wet mixture. Mix gently until just combined. Do not overmix.Kid-Friendly Tip: Kids can help with pouring ingredients, mixing batter, and scraping bowls.Bake the Cake Layers
Divide batter evenly between the two pans.Bake for 28 to 32 minutes, or until a toothpick inserted in the centre comes out clean.Let cakes cool in pans for 10 minutes, then transfer to a cooling rack to cool completely.Shape the Heart Cake
Cut the round cake in half.Rotate the square cake so it looks like a diamond.Place the two round halves on the top sides of the square cake to form a heart shape.Make the Buttercream Frosting
Beat butter until creamy. Gradually add powdered sugar, milk, and vanilla. Beat until smooth and spreadable. Add food coloring if desired.Frost and Decorate
Frost the cake evenly. Let kids decorate using sprinkles, candy hearts, or chocolate chips.