Oh here is a photo of the room from the staging when we purchased it. Note that the wall to wall neutral carpet will stay

If you are trying to use bedding with pink, red, purple, and blue you do not need any area rug to add interest. The room will be busy enough.

There's wall to wall skip the area carpet, unless you are hoping it will unify the bedding. In that case I like jck was thinking something with ALL the colors in it. I wouldn't invest a lot--this arrangement will be very short lived. We had a lot of different configurations when we had three kids...like you had girl/boy at these ages together when new baby arrived. Had all three beds in one room all toys in the other...eventually the girls shared and son was alone...it's not worth the money until the final stage is set...and by then it was only a few years until one was brave enough to take the downstairs room and all three had their own.

I agree this is totally a short term arrangement - littlest brother at some point will probably move in with middle brother and let big sis have her own space! I was thinking of an area rug to protect the wall to wall from kids who like play dough and markers and have a tendency to get both on the carpet…. So hoping for an inexpensive one that can disappear once they are a bit older :). I like the idea of “all the colors”. That hexagon pattern with all the colors is really fun!!

I think you can’t have too much colour in kids rooms! Would do a colourful rug with a bit of boho theme to go with cane & white beds