Well, I finally got the bodysuit to morph properly!  Thanks to all your suggestions, I believe I've made some significant improvements.  I decided to have a one morph for the head and one for the body.  The head morph makes the jaw slightly smaller and the forehead and eyes a little larger.  The body morph flattens the breasts, narrows the hips, thickens the neck, and adds a little extra bulk to the body.  I decided to leave the actual body proportions up to the built-in HeadSize, LegsLength, HandsSize, and FeetSize morphforms to make room for slight individual variation.

I think the youngest I'm going to be able to go with this is 5 or 6 years old.  The reason is that I can only make the head so big in proportion to the rest of the body before it looks too heavy for the neck.  I've thickened the neck as much as I could, but a HeadSize setting of 0.2 is about as far as I feel comfortabe taking it.  It would really help if there was a morph that would thicken the neck in the Z direction instead of just X (or maybe a bi-directional neck length morph).

Here's a test render of a re-done 7-year-old Francesca.

HeadSize: 0.18
LegsLength: -0.8
HandsSize: -0.07
FeetSize: -0.07
Minor adjustments to the hip of the bodysuit for best fit