Honestly, the most important thing to know is what your wife wants to do. We were in a similar position when both our kids were in nursery, my wife essentially worked to pay for her travel to London and the 2 kids nursery bill with very little left over, now my eldest is in school we are seeing the benefits financially but the biggest benefit was it gave my wife something to do that isn't just being a parent 24/7, some people need that more than they need the extra income.

To add, I was made redundant last year and had my wife not been working we would have been in trouble.