To go along with the Wii U's touchpad, Nintendo have announced plans to release an attachment that will let other players use a screen with their regular Wii Remotes.
The attachment will work a lot like the Wii U remote and will have touch pad capabilities. How it works is much like a stage light; the screen is made up of a small mirror that reflects light from an LED which then the controller will interpret as data. If a player chooses not to use the touchpad, they can still use the Wii Remote the same way you did before.
Parents may find this attachment quite useful when dealing with multiple children who wish to all use the regular Wii U remote. No release date has been specified for the attachment, but it will more than likely come out soon after the Nintendo Wii U's release.