Ignore the "Adult Coloring Book" in the title. This is perfectly suitable for kids as well. :)

Probably best with colored pencils. The coloring book contains 36 beautiful grayscale horses - thumbnails of each are shown in the sample images. The back of each page is blank. They are not perforated, but could be cut out of the book if desired.

Ruth Sanderson is the illustrator of the Horse Diaries books and many other horse books. The drawings included in this coloring book are amazing. Some of them are illustrations used in those books. 

Each of these images would serve as good sketching practice as well.

80 Pages
Dimensions: 8 1/4 x 11

You can find a tutorial for one of the horses from this coloring book on Youtube.