Reports are coming in from across Europe that Nintendo has moved to censor out 18+ games on the Nintendo eShop during day-time only making information and purchase available starting at 11pm until 3am.
The blocking of 18+ content is there regardless of your parental settings on the actual console and it is unknown whether it applies across all countries in Europe at this point. Regardless, we can probably assume third parties with 18+ titles on Wii U won't be dancing when they read up on eShop sales for those particular titles.