HISTORY AND FACTS ABOUT NUDITY
(This is family-friendly list of facts for older readers. However, some of the links/resources may contain images inappropriate to some younger readers.)
No matter how fun it is to run around (NAKED!) after taking a bath in the privacy of your house, most children understand that they need to put on clothes before heading out in public.
Not everyone in the world views nudity and the need for clothing the same way, however. In India, for example, tourists are usually advised to cover up their arms and legs to avoid getting negative attention. In Japan, there are some traditional bathhouses with communal/public bathing.
Complete or near-nudity is still common for some cultures in warmer climates.
NUDITY FACTS IN HISTORY
In ancient Egypt, children didn't wear any clothes until they were about six years old.
In Olympic Games in ancient Greece, athletes usually competed nude. Married women were forbidden to watch the Olympics under penalty of death (!).
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EXPLAINING NUDITY TO YOUNG PEOPLE, HEALTHY BODY IMAGE AND MORE
"Let's Get Naked!": Helping Children Feel Comfortable In Their Skin: from PhD in Parenting.
Teaching Nudity and Modesty To Your Children: by Mary Jo Rapini, Author/Speaker/Psychotherapist.
Explaining Your Family's Approach To Nudity To Your Toddler: by Anna Sharratt, Canadian Family.
How To Talk To Kids About Nudity In Art: from Mommy, Hungry! parenting blog.
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RELATED RESOURCES FOR OLDER READERS, TEACHERS AND LIBRARIANS:
Nudity In Ancient To Modern Cultures - by Aileen Goodson
Timeline of non-sexual social nudity (Wikipedia)
Nudity Throughout History - by Alexis Hauk, The Phoenix
Clothing Laws By Country (Wikipedia)
Culturally Correct Nudity - Travel tips for women on what different cultures around the world expect to be covered up (some of these facts are a bit outdated, I think).