"In the realm of 12- to 13-year-old girls, nothing much is voluntary, and the peer pressure is intense to conform and be part of it," Balkam said.
Maryland PTA president-elect Ray Leone said schools in the region are struggling to keep up with complaints and questions about online safety because children are moving so quickly between the latest social network sites. Counselors and educators have little time to monitor how children are using social media.
"It's hard to even get your head around any of these new sites. It's overwhelming for everyone I talk to," said Leone, whose own children, ages 15 and 18, are on Instagram, Snapchat, Twitter and Facebook. "Most parents are just throwing their arms up in the air because the new platforms are coming and going so fast, it's hard to get your head around it."
Middle school girls are particularly sensitive to online interaction. Positive or negative comments contribute to self-esteem and the formation of identities, experts say.
Racking up followers and "likes" on Instagram is a measurable way of feeling acceptance, said Simmons, the "Odd Girl Out" author. On Instagram, teens often post notes imploring the public to become followers and to "like" their posts.
Hollee Actman Becker, a writer and blogger from Philadelphia, last Saturday discovered her 10-year-old daughter was in an Instagram beauty pageant. Horrified, Becker confronted her daughter and realized the girl didn't fully grasp the risks of the contest.
Becker said she didn't know the minimum age for Instagram users is 13. She will let her daughter maintain her account, she said, but has pushed back against contests on the site. She posted a photo of the words "Beauty is Skin Deep" on the palm of her hand.
The photo is beginning to go viral.