the design. It actually worked nicely for one shirt, but was a disaster for any others I have tried. PROBABLY because my kids are quite heavy, and I have no "model" for small or medium sizes. I always end up with the design almost under the arm pit, or up closer to the collar bone. Is there some "formula" or something I can use for placing the design?

Hi Waterlily, I have an Embroidery Placement Guide that I sourced from EmbLibrary back in 2007, and I have just checked and it is still available, see attached link. They have placement guides for adults, infants, toddlers & children. I have used their measurements a number of times and they have always looked good.
Cheers, Claire

Usually when measuring for placement on any shirt when it is on the side (breast) is take a ruler & place the edge of it on the base of the underarm heading toward the centre of the shirt... that gives you how far down from the shoulder to place the embroidery. Now, measure 2/3's across to the centre of the shirt & that should give you a good idea of placement. Also, have a look at shirts with a pocket on the breast (men's business shirts) you can measure percentages from under the arm & how far down from the collar they are. I have found that when people want embroidery on a shirt, they usually have it either on or on top of the pocket (level & centred with pocket). I hope this helps.
Regina