I may be in the minority here, but I like a little more focal length when shooting babies. They're small after all, so I want a narrow FOV. On a camera like the rebel, I'd like to use a 70-200 zoom or an 85mm prime (budget will determine aperture- the faster the better IMO).

The best part is, when the kids get bigger, these same focal lengths work great for portraits with a full frame camera. Isn't that a great excuse to upgrade your body 3-5 years down the line?