Important to think about as well is the maintenance and clean-ability of the finishes. ie: semi-gloss paint is much easier to clean.... versus matte paint. Wood versus synthetic materials etc. Carpet versus hard-flooring. etc.
AND, keep in mind the adaptability... ie: as the kids grow older... will you have to do mega-changes again in terms of decorating to suit their ages... or not? The taste/needs of kids changes too. So keep that in mind.
But for storage... have something theme oriented or not? Which will be easier to grow with the child or not? "Built-in" wall cubbies, versus storage shelves? Shelving/closets with doors, or open shelving?
Also the height of things changes as they grow too.
A good thing to include in a kids room... is a desk as well. So they can study or do things in their room. Kids love having their own desks. And providing good lighting so they can read etc.
For the bathroom, there is tile, linoleum, stone etc. All with varying cleaning ease or not.
I have found, that a kids 'like' of character/themes changes each year. So buying kid shelving that is say "princess" themed really gets outdated quickly... then it just sits there and doesn't "grow" with the child. So for 'themed' rooms per gender/child... perhaps decorating with smaller items like pillows/lamps/wall pictures/area rugs, are more "flexible" and changeable.... versus having the "theme" be in terms of major or expensive "furniture". So thinking ahead... also think of the flexibility of the "furniture" in their rooms... etc.
Just some quick ideas,
Susan