This popular Valentine’s Day science activity is a holiday variation of the classic magic milk experiment. It’s a little bit science, a little bit art, and a whole lot of fun!

*This post contains affiliate links. Please see our disclosure policy.

Magic milk is one of our favorite science activities because of the endless possibilities for creation. The kids love watching the colors erupt, scatter, and mix. It is sometimes unpredictable, which makes it exciting and new each time. Add some heart shapes and you have a Valentine’s Day science activity that is irresistible.

Magic milk hearts is a Valentine


Milk (We used whole since that is what we had in the fridge, but any kind of milk will work.)

A bowl, casserole dish, or baking sheet

Food Coloring or liquid water colors (Especially red, pink, and purple for Valentine’s Day!)


Heart cookie cutters – Use these to make Valentine’s Day window gel clings when you are done with magic milk!

Liquid dish soap


Magic milk hearts is a Valentine


  • Place a heart cookie cutter in a dish or baking sheet.
  • Pour milk into the cookie cutter. It will leak out into the dish, and that is fine. You don’t want or need much, just a thin film that covers the bottom.
  • Squeeze a few drops of food coloring or liquid water colors into the milk. Add glitter, if desired.
  • Dip the end of the toothpick into the dish soap and then into the center of one drop of colored milk. Don’t stir it! Watch the color erupt and swirl inside the heart.
  • Repeat and enjoy.
Magic milk hearts is a Valentine

Valentine’s Day Science Explained

Why do the colors explode when you add dish soap to the milk?

Put simply, the dish soap interrupts the molecules at the surface of the milk, making them spread out. This makes the colors spread out, leaving a beautiful marbled pattern behind. You can read my full explanation here if you are interested. The science behind what you see in magic milk is pretty fascinating!


Sign up for our Monthly Newsletter!TinyLetter


Learn with Play: 150+ Activities for Year-round Fun & Learning is a giant collection of hands-on activities for babies through kindergarteners.
Science books for kids from Usborne

STEM Saturday

Best Structure Building Activities for Kids from Little Bins for Little Hands

Eiffel Tower STEM Challenge from Preschool Powol Packets

A Heart Shaped Math Puzzle from Handmade Kids Art

Animal Camouflage Hands-on Science Activity from Stir the Wonder

Valentines Themed Density Jar Experiment for Kids from Lemon Lime Adventures