Just talk to them. You have a month, right? Talk to them. Let them know what is going on... don't wait and spring it on them with only a few days left to process it. They will need time to process it.
We moved from the only house my kids ever knew when they were JUST turned 4 and ALMOST turning 7. And they asked Sooooooooooo many questions. Many of them multiple times. They just needed time to process the whole thing.
We built our house, and lived in a rental for about 10 months during the construction process. They did not change schools with the move. But we visited the construction site every week (sometimes more often) and they were able to SEE it and the building process. And as it got closer and closer to being finished, they had more and more specific questions about the move: where is my bed going? Will my stuff go in that closet? ALL my stuff? What about the stuff in storage? Are we leaving it there? Can we visit the rental? Will we have all our movies? Will we have a yard? Can I walk to school? Will I be at the same school? How will we get our mail? Can we visit our old house? How will Nana know how to get here? and on and on and on and on....
Sometimes answers beget more questions.
Some days there were no questions. Some days it was the same 2 or 3 questions as the last 2 or 3 days before...
Just be matter of fact, explain you are moving to a new house to live in. Maybe explain some of the reasons you want to move there. My kids are very sentimental, and wanted to take pictures of our old house. That was where all their memories are from! I highly recommend doing this!
Take pics of ALL the rooms, the yard, the front of the house, the back of the house, the view of the neighbor's,etc. My son's favorite part of our old house was the closed staircase to the bonus room over the garage, where he rarely ever went. But he loved it.
Take pictures and make them a photo album. Maybe label it "our first house" or something.
ETA: Yes, if you are willing to let them choose their room color (retaining veto power, of course) then that is an excellent idea. We did that as well. I actually got a piece of posterboard and taped the paint chip cards that we were considering all over it (to make sure they went well together from room to room, and to put the 2 or 3 we were considering for one room together in one place while we slept on it/ thought about it).
My then 4 yr old daughter chose violet for her room (it actually looks like hot pink with just a little blue in it, so not hot hot hot) and my son chose barn red. Daughter took awhile to decide between that and a lavender color, but eventually she did decide.
It was also nice to let them HAVE a paint chip with their chosen color on it, in advance.