Scary times. I remember that moment all too well. It didn't go well for me and my wife subsequently left me for another man and outed me to anyone and everyone who would listen to justify her cheating on me. I went back into the closet and spent the next 10 years being a father to my children. I felt that I needed to be there for them in the simplest way. My needs as those of many other parents had to take a back seat for a while until I felt they were emotionally and psychologically ready to handle my transition. I put that at the time my youngest turned 18. The upside of my delayed transition was that I now have a great relationship with both of my children and they appreciate the sacrifice I made to consider their needs before mine while they were small.
I know a lot of Trans women who haven't fared as well with relationships with their children. I can tell you that whatever the cost, you will never be 100% happy if you alienate your children or lose your relationship with them.
My advice is, to be honest with your wife, but make the transition slowly. Take care of the electrolysis or hair removal and perhaps take a low dosage of androgen blockers so you can refine your body before making the "big" leap. I think having a long view and doing things to transition incrementally over time is a way to keep both your sanity and your family intact.
It is hard to see the other side of the shore immediately anyway. I think it's far wiser to make sure you have your bridge almost entirely built before laying that last plank. Then the leap and surprise are not as great as they might have been.