You will need to resync the remotes. First you must clear the Wii of the sync's that you have established.
Turn the Wii console power OFF by pressing the POWER Button on the front of the console. Unplug the power cord from the wall outlet for a few seconds. After a few seconds have elapsed, plug the cord back into the wall outlet.
Turn the power of the Wii console ON. When you see the Health and Safety screen, open the small flap on the front of the Wii console to find a red button labeled "SYNC." Press and hold the SYNC Button down for 15 seconds. This will clear all the syncs on the Wii, allowing you to get a clean start to begin the process described below
After holding the SYNC Button on the Wii console down for at least 15 seconds, you can now "re-sync" your Wii Remotes:
With the first Wii Remote you wish to sync, remove the battery cover on the back of the Wii Remote to find a small red button just below the batteries. Press and release the small red button just below the batteries on the Wii Remote; the blue lights on the front of the Wii Remote will blink.
Quickly press and release the red SYNC button on the inside of the white flap on the front of the Wii console
When the Player LED blinking stops and stays lit, the syncing is complete. The LED that is illuminated indicates the player number (1 through 4). This sync procedures must be followed for each additional Wii Remote added to the system