Whether you're an elementary school teacher, a homeschooler, or simply a parent looking for great books to share with your children, these well-written and respectful books about the late, great Martin Luther King, Jr are the best literary resources out there for teaching about his life and work. I've read stacks of children's tomes about Dr. King, but these three are the ones I come back to again and again.

A Picture Book of Martin Luther King, Jr. - David A. Adler
Perfect for the youngest of learners, this picture book manages to be kid-friendly without dumbing down the content and informative without being boring. Good for early readers (I'd put it at about ages 6 - 8) and a good read aloud for all ages.
Martin Luther King - written by Rosemary L. Bray, paintings by Malcah Zeldis
A more detailed account of Dr. King's life, this book is beautifully illustrated with full-page folk paintings and follows all aspects of his life and work, including his time in prison and his tragic death; all events are dealt with tastefully and with great respect.
I Have a Dream - Martin Luther King; foreword by Coretta Scott King
I looked high and low for a picture book that contained nothing more than the text of Dr. King's "I have a dream" speech and was thrilled to find this one. With a foreword by Coretta Scott King, each part of the speech is illustrated by one of 15 award-winning artists. Pair this with a video or recording of Dr. King's speech and you've got a moving, memorable, and accessible way for young children to learn about one of the most powerful American speeches of all time.