By necessity, since they are at the mercy of their parents, children are usually very perceptive in this regard. They undoubtedly noticed something was going on. I would tend to favor a 'need to know' rule for the time being, as they will pick up on any positive changes on their own. No need to worry them with your problems just yet unless they inquire, IMO. That said, I do think that some sort of conversation on the subject should occur at some point, but preferably once you have the situation under control.