In a large bowl, place your baking soda and slowly add water, mixing with a spoon first and then your hands to get it well mixed.

Add some red food coloring and glitter.

Place your cookie cutters on a baking sheet or another pan.

Press your mixture firmly into each cookie cutter to fill.

Place in the freezer for a couple of hours.

Remove the hearts from the freezer.

Provide your child with a bowl or cup of vinegar and droppers or syringes.

Let them slowly add vinegar to the frozen baking soda heart.

Kids will love watching how the two react together to change in texture and shape.