The same survey also found that of the 20 million minors who actively used Facebook in the past year, 7.5 million of them were younger than 13 years old, though Facebook's terms of service require users to be at least 13. More than 5 million of these minors were 10 and under.
Additionally, the survey found that 1 million children were victims of cyberbullying.
Amy Stiefel, 16, is one of those children. She said she felt terrible after receiving mean posts on her Facebook page.
"I just felt attacked by a whole bunch of people, for everyone to see," Stiefel said.
Devastated by the cyberbullying, Stiefel joined Love Our Children USA, a nonprofit group that promotes Internet safety.
"We project that more than 5 million kids ages 10 and under had Facebook accounts last year, even though 13 is the minimum age that Facebook allows," said Rosalind Tordesillas of Consumer Reports. "We found most of their parents did nothing to monitor their Facebook activities."
"In order to protect your child, whatever their age, it's important to supervise their Facebook use," Tordesillas said. "Become their friend and check their profiles regularly. You can also connect their Facebook account to your email so you see incoming messages."
Facebook users of all ages should use privacy settings. But one in five active members had not used these settings, according to Consumer Reports' survey.
A user can set them by going into the privacy settings area and selecting "Friends Only." It's also important to use the privacy settings on the apps and websites linked to the account.
"If you connect your Facebook account to another site, you're allowing that site to collect a lot of your personal information unless you block its access," Tordesillas said.
The Consumer Reports survey revealed other troubling facts about Facebook, including that almost one in three people have "friends" they are not completely comfortable with. Six percent also admitted to having a friend who makes them uncomfortable about their or their family's safety.
Last month, Facebook established new ways to report bullying online. They say users can report the problem to Facebook, block the person who posted it or contact help.