Wow, some harsh comments here, and at one of our own this time.
Just because a man works while a woman stays home with a kid doesn't mean they are locked in the shackles of traditional gender roles.
On the other hand, the best people to make a decision is the two people involved. There are a lot of choices and you have the most information about what will probably work best. So you do need to talk to your wife about all this, some time in conversation between now and when it's too late
Feelings do change after you hold that baby in your arms - so build some flexibility into your plans.
Savarel has given adequate justification as to why his wife would be the one staying home, so there should be no need to drag this into any more of a 'gender role' argument than what it already is. Please offer non-judgmental financial advice to Savarel, or move on to the next thread.
My own advice would be do go with what works for you and your wife, and save up as much as you feel is necessary to get you through the time off work. My wife and I have two kids, and both times it was my wife who stayed home for 3 months with them -- partly because I make more money than she does, and partly because of the biological needs of a newborn child -- ones that can only be provided for by a mother. You can call it nature, or you can call it the work of the deity of your choosing, but there is a definite bond between a newborn child and the parent that has carried it in their womb for almost 10 months.
Both times we scrimped and saved every penny to build up enough to cover her 3 month maternity leave, and had nothing left by the time she went back. I wouldn't advise that anyone cut else cut it quite so close, but we survived, and that is what matters. It seems a little extreme to think that you must have well over a year's worth of emergency fund in a bank account in order to have kids.