Open the System Settings software from the HOME Menu.
Controls & Settings guide
Through the use of a Parental Controls PIN you can tailor/restrict Internet Browsing, Nintendo 3DS Shopping Services, Display of 3D images, Sharing Images/Audio/Video, Online Interaction, StreetPass, Friend Registration, and DS Download Play.
A Nintendo account (email address/Password)
See more resources and articles to help children stay safe online.