Kidshealth.org has created a teachers' guide on sleep for you to use with your classroom. Intended for grades 3-5 but can be modified.
Kidshealth.org has a parent page devoted to growth during sleep. Visit it for details on the needs of kids at different ages, sleepwalking, and nightmares. Great resource. They also have a section specific to sleep in general.
And just in case you want it, here is the student page on sleep from KidsHealth.org.
Busyteacher.org has a free worksheet title A Good Night's Sleep. It begins with a text all about the importance of sleep and then has comprehension questions specific to the text. Also included are a sleep record page and an answer key. Intended for grades 3-4.