The Wii U's Nintendo Network is not entirely free. According to a Wii U support page, parents or guardians must pay a one-time fee of $0.50 to create a Nintendo Network account for children under the age of 13. This acts as proof of consent to create a Nintendo Network account, and is in accordance with the Children's Online Privacy Protection Act (COPPA).
According to Nintendo, credit card information will not be stored on the Wii U. Additionally, because this information is not stored, gamers must re-enter their information to make purchases through the eShop.
Parents and guardians with multiple children will not need to pay the fee again to create additional Nintendo Network accounts. Once the first child is set up, the Parental Control PIN is the only information needed to create additional accounts.
The Wii U launched today in the United States. For more, check out GameSpot's coverage of the Nintendo World launch event and reviews of Nintendo Land and New Super Mario Bros. U.