First of all, the Wii was a not a kids console it was a family oriented console. The Wii U , on the other hand, is not - have you even looked at it's library?
Darksiders 2, Mass effect 3, Tekken Tag Tournament 2; just to name a few examples that are not kid games and they exist for the Wii U.
The problem the Wii U has is that there are barely any games for the system, those that exist are mostly ports and because of that people don't want to buy the Wii U since they already own these games. In result developers don't want to make games for the Wii U because it sells too poorly. It's a catch 22.
Nintendo needs to publish a few games on their own to encourage gamers to buy the system so third party developers will make games for it. Bayonetta 2 will most likely help in selling Wii U's which is a step in the right direction for them but it will take a while until it gets released.