What an interesting idea! I have not read
Sylvie and Bruno but am wondering if this is the story you are referring to..... Click
here for text. Here is the same book for sale (new and used) on
Amazon.
I assume this book is out of copyright since it was first published in 1893, just a year or so after Tolkien was born.
I do have some general thoughts on hobbits and where they came from in terms of JRRT’s mind, but will try to post later on that.