Easy Simple Paint Ideas for a small Girl's Playroom, Castle & Landscape

So the hubby is nearing the end of replacing the ceiling & some walls in the girls playroom. I have been busy sketching out ideas to paint on their walls. The room before wasn't bed, but I' not gonna pass up an opportunity to make it even more fun!
Here is there room before:

There is a lot crammed into 7.5' x 12'. The major pieces of play furniture will stay. Moving out the large wood desk. Lots of artwork on the walls & some damaged posters that are ready to retire. Time for a refresh!
Entire home floor plan below with playroom out to right.

Since the space is small & only has 1 window, I want to create depth with light colors. I also want the design to be flexible for many years of changing fads for them. AND I want it to be simple to paint! Is that asking too much?
I have asked CAT & DOT what they want. Castle & Angry Birds! OK, time to brainstorm.
Here is my outline of the blank walls. I repeated the smaller side walls A & C so I could gt a feel for how the design will wrap around the room.

Did I cut & paste pictures of the actual toys from the girls room? Yes I did! lol
The programs that I used are Microsoft Paint & PrintMaster 2011, a gift from my Mother in Law, TY :)
Most of the work could be done on Paint only.
So now on to Angry Birds first. They have cool backgrounds. Here are my favorites that I cleaned up with Paint.

I like the grass & sky theme. It is adaptable & playful. The striped sky with 2 colors of blue was an early YES for the design.
But the grass on these seemed too complicated. I found these images:

I like the simple broad stripes that give depth & are easier to paint. So I combined them & came up with this.

Perfect shapes! (We'll get picky with color later) We can hang Angry Birds or castles or trees or whatever!

Now onto the castle. CAT & DOT want a pink castle. I want to make a costume closet for their many costumes. So a castle wall/room will be the perfect princess backdrop.
Searched all over the web. Castle walls that are simple are hard to find. I had to design my own. Yeah! :)
I picked out an irregular stone pattern (to look old castle like) that was square, easy to paint with tape!

The grey picture I redrew out to the pink wall on Microsoft Paint. I liked the pink stone with light pink mortar the best.
The wall is a great backdrop, but I needed a transition to the sky & grass. I tried balconies, windows, broken stone. None looked right or were easy to paint. After several days & dozens of drawings I finally decided on simple towers. Here are the best one I found for easy painting.

I settled on the rounded top. Here I experimented with width & wrap around design.

I haven't put a sun in the design because I may put one on the ceiling or make one to hang on the wall.

Ok let's refine the design next post! See ya then :)