Well, I wouldn't be surprised. They jumped into living together and having a child after knowing each other for a very short time. I've dated guys longer than they have been living together and couldn't say that I knew those guys well enough.
I wouldn't be surprised if they eventually break up. They are a Hollywood couple after all, with dueling egos, careers and the stress of a new baby on a new relationship. I hope they work it out, but the odds are against them.