Dear Robb,
I make shoes and boots all the time. Mine are for my authentically dressed dolls, but the process is the same whatever the size.
The sole comes first. The sole determines the shape of the finished shoe. If you're making shoes or slippers for a toddler, you need the toddler. Trace around the foot. Take a paper towel, and drape it over the baby's foot, taping it to the sole (best done when the child is asleep). This accounts for the ease needed to fit smoothly over the child's instep.
For the first pair, you probably don't want to get much more complicated than this, in which case, continue the toweling around to the back of the child's foot, pin or mark a center back seam. This gives you the "upper."
Take off any seam allowances you might have, and tape the pieces together. Try them on to make sure you don't need to make any adjustments. Now trace the pieces onto new paper, and seam allowances. A 1/4-inch seam allowance is OK for the uppers, but add more to the part that attaches to the sole, to make it easier to sew. The uppers need to be interlined with cardboard or plastic (to keep them washable) called "foxing." The toe foxing is shaped like the toe upper, but has no seam allowances and is glued in place above the seam allowances. The heel foxing is shaped like a half moon, following the shape of the back sole, and coming up to the heel tendon. The heel foxing is glued on after the center back seam is sewn.
Starting at one side of the heel, hand gather the upper all the way around, using more gathering at the toe and heel areas. Insert the insole, and pull up the gathers to hold it in place, then sew back and forth over the sole to hold the upper to the lower. Then glue on or sew on the sole. I used to cover a piece of cardboard or plastic with black cloth for the sole, then sewed it to the upper. I now have a large stash of thin leather, and I just cut a piece and glue it on for soles.
This may be more complicated than you want to get, so go to a re- enactment site and find a moccasin diagram that shows how to make a moccasin with one piece of leather. It will have puckers and gather, because that's how they were made.
Teri