Right now I am going for moonrise towers quests and beating Ketheric, then I want to go to the creche. I hope it is possible because I want to do both in order to open up opportunities for later.
Once you pass through a certain pool in the "Find the Nightsong" quest, you won't be able to access the creché or other act 1 locations anymore. This locks you out of several quests as well, so be careful.
