Kids LOVE paint! Let your artists set up their own palette of paint!
As we empower young artists to create unique artworks, we also need to equip them with the skills to acquire their own materials in a responsible manner. Posters such as this Tempera Paint Palette Poster give solid reminder to not waste the paint! I always say "size of a quarter or SMALLER!" Students apologize when the paint comes out fast on accident - they know the size of a quarter, and know when they've overdone it!
In my classroom, I let students know that they can ALWAYS come back to the counter to get more paint if they need, but that I can't get it back in the bottles. We use paper plates for our palettes (but you could use plastic if time allows for students to wash their own palettes at the end of class - I love the lids from the big tubs of ice cream!) I find that students are much more apt to experiment with paint mixing on a plate. I introduce this in kindergarten to set up good habits early - so they aren't mixing everything together in one giant slop on their plate. I also have students share their palette with at least one other person. This way they learn to mix paint without using up all of one color. (I'll need to make a poster about this next, won't I?!)