I take it you've not made a bow at all before trying one of these.
The methods are the same, and you just need to downsize things, and be a touch more careful (a minor slip of a knife will not cut a regular sized bow in half

) so the starting point is much the same.
Start simple. Go read
Sam's site on making bows and mainly use the
Red Oak build along.
If you are not going to "back" your mini, and make it a self bow (Backing of a thinned glue would suffice though) make sure you follow a ring up the back. Otherwise, tillering, and the shapes and design are all applicable. Just remember it is far easier to over draw such a small thing.
Willow will make a slightly weak bow, but it is tough, and will probably look great when done.
Are you using a new growth branch, or a bit of older, smaller grain?
Some woods, a bow is made from nearly one growth ring, using a bit of small branch, you could even split off mini staves, and go for an elb, or other self style design.
Bamboo works great for little ones as well, as you are working within the wall, so it is like the old fiberglass bows.