Nintendo's social hub Miiverse won't let kids aged 12 and under send friend requests.
This was announced in a quiet fashion in the Miiverse's latest update. Nintendo, for its part, said it has implemented this limitation in order to protect younger users.
Here's what's written on the updated Miiverse Code of Conduct found in the User Menu and by clicking on the Settings/Other option:
For the protection of younger users, direct friend requests are not possible in Miiverse for users aged 1 and under. At the same time, younger users can make friends on Wii U outside Miiverse by entering each other’s Nintendo Network IDs in the friend list on the Home Menu.We encourage younger users to make friends on Wii U only if they are friends in real life (such as friends from the same school or neighbourhood). Therefore, do not attempt to exchange your Nintendo Network ID with other users on Miiverse.