I had the 2nd graders learn about tints and shades as well. This was challenging for them, but they were able to grasp adding white for tints, and loved mixing more colors.
Next, we had a fun day of just mixing colors as each student engaged in the challenge of "how many colors can you mix from just three?". I also gave the kids white paint on their palettes, so they could mix tints. The kids absolutely LOVED making these color swatches. I think doing this from the start without doing a color wheel first would also be a fun way to explore color mixing, especially if the students recorded their findings like scientists (and artists) and shared them with their peers.
I wish I had a photo of just how many swatches were made by all three 2nd grade classrooms. This is only a fraction of the total. It was so wonderful to hear the students sharing how they mixed a certain color with a friend, as they mixed even more. They also offered each other advice on how to get a certain color.
I also had the upper grade students learn about and mix secondary, tertiary and complimentary colors, so that they could apply that knowledge when painting their masks. The color wheel above is more complex than the one the 2nd graders used.