I did not ride before my kids were born, I took it up when they were 2 and 4. My commute is 12 miles each way, and I think it's about perfect, one hour each way and no need for any other exercise afterwards. But here's the rub. One of the reasons I took up commuting was because it was a way for me to get exercise in without interfering with family time. Don't think that you will just start riding more on the weekends. If your experience is like mine, once you're home, you're home, and you won't know from one day to the next what you are going to come home to, sleeping wife, sleeping baby. Everyone crying and screaming. Wife crying, baby sleeping
All those scenarios. And when you get home, she's been there all day and is ready to hand you that little bundle of joy (which is truly a joy). I gave up golf when the kids were born because I no longer wanted to spend half a day on the weekend chasing a ball around. My commute by car takes a minimum of 20 minutes and could take the full hour or more, so riding the bike instead does not really add to my time away from home. After a long week at home with the little angel, your wife may have a list of things she wants to go out and do on the weekend while you stay at home. You can also make an arrangement, that you get a long ride home from work and she gets a nap when you get home. But from my experience, as I said, once you're home you're home, and it's great, just plan accordingly!
Congrats!