The first lesson I will share is this one designed for kindergarten, but suitable for pre-school or first grade with some accommodations for younger learners who may not have developed sufficient skill with scissors yet.
Step 1: In separate trays (I used the trays from microwave entrees) place the different paint colors and several marbles. Give each student a similar tray with a piece of paper that fits snugly in it (about 3 x 5"). Have students rotate between the three colors. They select one paint covered marble each. drop it on their papers in their trays and roll the marble around. Repeat with each paint color. Then repeat the process again on two more pieces of paper in different colors than the first.
Step 2: While the paint dries read a color-related story or a story about Jackson Pollock (the artist of inspiration). The color-related story I read was White Rabbit's Color Book by Alan Baker. It is a cute story about how the primary colors mix to form secondary colors and how all three combined make the color brown.

Step 3: By the time all students have washed the paint from their hands and listened to the story the painted papers should hopefully be well on their way to being dry. As they continue to dry distribute three more (3 x 5") papers, heart tracers, pencils and scissors. Demonstrate how to fold the paper down the middle, trace half a heart on the fold, cut while folded, and open up to reveal an open heart frame. Provide extra help with proper cutting, especially for younger learners.
Step 4: With the painted papers fully dry, have students glue their three cut-out frames over their three marble paintings. This will hide some of the paintings, but explain that this is okay and what is to be expected. Then mount the three finished framed heart painting on a larger sheet of paper either vertically or horizontally, whichever you prefer.