I have the exact same problem. As much as I love bangles and bracelets in general they never fit me. So I also buy kid's bracelets. The bad thing is that it is very hard to find nice ones. Here, in Europe there is Accessorize, which has stores almost everywhere. It makes great accessories for kids and I have some very nice bangles from there. I don't know if there are Accz stores in the USA.
I would be very interested in finding more places that sell bangles in small sizes so if anyone knows anything else or some online store I would be very grateful.