Setting up shop! Elements of art murals

Since we have moved into our home about 18 months ago, the basement playroom has had almost no attention in regards to decor. Over February break I started the remodel.
I knew that I wanted strong art elements. Both of my children enjoy projects and I want those skills to carry over into multiple areas of play. The designs needed to be simple and display various types of expression. I decided to use the elements of art as the foundation for my designs.
I was inspired by multiple forms of design. An item from etsy inspired a bubble painting that showed color mixing. A wall decal set inspired a tree house that shows organic and geometric shapes. This one is placed above a small cubby area that is being padded,  filed with pillows and stuffed animals, and quiet toys. The "tree house" will be a quiet hangout spot. 
Two pieces are not yet finished. A company brochure inspired mountains to show how lines can be used to fill space,  rather than simply define space. I am using 1/4 inch painters tape to help create the lines. That should be competed later today. I will update this post when it is finished.
I used clip art to create the shapes for the trees of my value study. It is doubling as a display of value and to show progression of the seasons. The bright yellows of summer fade to darker neutrals of fall and cool winter fades to fresh greens of spring. I have only done the preliminary sketch for that piece.
I also have plans for a texture study. There is a fireplace in the room that I am going block with an inset board. I'd like to do a little cave scene with animals similar to Jan Bretts' book The Mitten.
How have you used art to inspire your children's play space?
A blurry photo of the balloons... The overlapped portions show mixed colors.
Tree House - AKA - Cozy Corner
Mountains: large outlines and beginning tape to make the fill lines
Preliminary sketch for color & value scale trees