Start Co-op on Disney Infinity for Wii U

My daughter got a second character for Disney Infinity (Venelope and she already has Wreck-it Ralph). Allegedly you can play co-op like this in Disney Infinity. But we have a second controller and hit + and we cannot get it to switch to co-op mode.

Any ideas what we might be doing wrong?

Does anyone have an exact step-by-step of how you do it? (This doesn't exist online after searching for hours.)

Solution 1:

We finally found the answer. You must have a Nunchuk connected to the controller. If you don't, it doesn't tell you in any way. It just won't connect at all.

Also, I found that it never works on the Wii version, except in Toy Box, but that limitation does not apply to the Wii U.