I made this pair of little boots for my son to wear this winter and I made up a little tutorial; it's my first tutorial so I hope it's okay.
You will need 3 pattern pieces: one for the top of the foot, bottom of the foot, and around the leg. I literally traced my kid's foot to make the bottom and wrapped notebook paper around his leg for the leg part and cut out a little half-moon. Not sure how I came up with the width for the top of the foot but it needs to be a bit wider than the bottom. I then added some room for seam allowance and some more for growth- if your kid grows like mine you'd better make it big if you want it to fit for more than a week!
I did the whole thing in fleece, both outside and lining, but you could line it in a contrasting fabric, or if your kid's a walker you could put a leather sole. You will need 4 of each pattern piece, 2 for lining and 2 for outside.
After you have cut your pattern pieces, match up the backs of the leg piece right-sides together and sew to create a tube. Next, get the piece for the top of the foot and stitch the straight
side of it to the little half-moon cut-out of the leg piece. I suggest pinning it if you're picky about it being perfect or if you're newish to sewing, since you'll need to ease the curve to fit the straight piece. I didn't pin it because I'm a "meh, just sew it" type of gal. :-) I used a wide zig zag with a short stitch length, which I suggest if you don't have a serger, because you'll need to stretch and manipulate it a bit to get it on (why do babies always curl their feet into little balls when you try to put shoes and socks on?)
You will have something like this:
Now sew the bottom of the foot onto the top you've created, right sides together, matching the back of the heel with the seam on the back of the leg piece. Again, pin if you need to.
You will have this:
Do all these steps again to assemble the lining so you have two identical boots. Insert the lining, wrong side out, into the outer layer, right side out, so the wrong sides are both hidden in between the layers.
Fold the tops of the layers into the middle, pin and stitch. I switched to a straight stitch for this step and added some trim.
And you've got boots! You could use different materials to make them warmer, more waterproof, cuter, etc.... this is a pretty basic pair.