Ask HN: looking for advice for a children's books online store

Dear HN,

I am settled to help my friend, whose small offline store of children's books is shutting down, and create a small online store for him. I have a clear vision of my "ideal" online store for children's books. One thing that makes me worry is that I haven't seen such "specialized" (or niche) online book stores. It's either Amazon-type or nothing. Have you seen, or shopped in, any book store that concentrates on only one type of books? Or is it completely hopeless? (I'm going to make it anyway though :-)

P.S. We're located in the coldest part of Russia.

Thanks!