Reports on the official forums this morning are that those who completed the Dalaran orphan's quest (Oracle pet/Wolvar pet) last year are currently unable to start the quest again today. Blizzard has already chimed in with a response:

This annual reset glitch has happened a few times in the past with other seasonal events. This issue should not be affecting the Stormwind, Orgrimmar or Shattrath orphan quests. It should also not be affecting those who are doing the Dalaran orphan quest for the first time. More information about the current seasonal event can be found in our Children's Week guide updated for 2010.

We'll update this post when Blizzard announces the fix.