I am an elementary art teacher, and I ain't scared. I can have my Kindergarteners (usually a class of about 30) paint. YES, TEMPERA PAINT! I'm sure you have your favorite way to manage paint in your classroom, but here is the method I've found to work the absolute BEST.
First of all, I love tempera cakes for littles. For the big kids, not so much. The little ones though do very well, and set up is minimal. Firstly, I have seven tables in my classroom. On each table I place a tray (I bought these from School Specialty, but you could use muffin tins if you prefer. They're the perfect size.) And in each tray are ONLY one color of tempera cakes. Each table though, gets a different color.
Next to the paint, I place a large cup with a wide bottom with brushes in it. NO WATER. I hate for paintbrushes to soak in water, for many reasons. But with the littles, they inevitably tip it over, so I just don't give it to them. :)
Here's how it works. During my instructions the paint and brushes are on the table, but the tempera cakes are dry. After my directions, I then squirt water into each of the paint trays using a little squeeze bottle. Once a table has wet paint, I let them get up to get their art shirts. I usually don't give them water until they show me where they've written their names on their paper. This accountability is good for them, and they've begun to police each other.
After they are shirted up, they can use the brushes on their table to "dab, dab, dab" in the wet paint, and "brush, brush brush" on their paper. My colleage uses the phrase "tickle the paint" and I like that as well. After they are done with the color at their own table, here's the trick. They put that paintbrush BACK IN THE CUP. Then they pick up their paper and MOVE TO ANOTHER TABLE! I have children wandering freely around my room, and the paint doesn't get mixed up because the brushes live next to the paint tray, and stay with their own color.
I wash the brushes at the end of class, because I still don't really trust Kinders to do that. Maybe one day. Dream a little dream.
Clean up is easy too. I give a couple kids the job of returning the brushes and the paint trays to me. (More on how I assign jobs later.) And then I go around the room and when a kid is in their own seat, I give them a baby wipe. We then have a "dirtiest baby wipe contest." This keeps the kiddos from throwing away their wipe when it still has wiping power. I can also tell who is actively looking for paint to clean up. And they LOVE this. Whoever has the dirtiest baby wipe usually gets a little perk, like an extra big behavior buck or a sticker or whatever.