Modesty is natural. Nobody has to work to teach children to cover up in front of people. They catch on early, and, if you want to see fast movement, burst in on a 6-year-old in the bathroom.
Our culture works VERY hard to overcome that natural tendency to maintain bodily privacy in front of strangers. Many, many network shows use young people (and actors playing younger) to systematically break down children's modesty.
The results can have devastating consequences.
Women, don't take naked pictures of yourself for the titillation of boyfriend or husband. Men, likewise, and also, don't keep those photos - if she sends them, delete them, and send her the link to this for the reason why.