The perfect time for family photos?

When people bring in their children to me for photos, I often ask if mom and dad would like to be in a few shots. After all, once baby arrives, it's difficult to get everyone in front of the camera at the same time. It's usually either mom or dad that are snapping away. Often, when I suggest that both mom, dad AND baby be in the shot, I hear "Well, I don't know. I haven't lost all my pregnancy weight yet, so I'd rather not"

I came across this blog post via another photographer. It's a great read, and so very true. is there a perfect time?