Hi Stacey! Coloring pages are a great idea to send to your child! The size of the envelope does not matter. However, each flat paper gift item should not be larger than 8.5" x 11". Regrettably, if the coloring pages are larger than this, then we cannot send it to your child. You can also send letters, photos, postcards, greeting cards, mazes, and dot-to-dots! There are so many wonderful options to bless your sweet girl with :). Thank you so much for your heart to bless her with your gifts!