hello from Washington state! No you really do NOT have to worry about mold in AZ. You can mist away with little to no problems in good ol AZ! I lived there for 52 of my fifty three years of life! Had hundreds of chickens. Really you should change the straw every month or there abouts. It's just better hygen for your birds and straw is very cheep anyway. They tend to poop it up if you leave it longer anyway. While I'm at it the only vaccine I use is for merriks if I spelled it right?
But like many of the other posts have stated its a very good idea to shade, shade shade and more shade in that HOT az sun. Always provide plenty of good clean water or you can lose a whole flock in a single hot day! Myself I like to keep a couple of back-up water sources as I feel it's that important in AZ!!!!!
Enjoy the kids enjoying the birds! Chores are great reaponsability learning tools and yes you MUST check to be sure they did what they told you they did!
Best of luck with your backyard babies!!!! Big Scotty
We have fungus, valley fever here.. Mold, fungus, bacteria ect... It is always something.. Where in Washington ?
What breeds do you have now ?