My colleague Barbara at March House Books has a lovely display on her website - see here. I can also recommend Peakirk Books and Stella and Roses books for vintage children's books. The lovely Jane of Jane Badger Books can supply you with vintage pony books at all prices and her website is mine of information and reviews.
I sell a small amount of children's myself too on C L Hawley Books. Go to our browse categories page and under C you'll find several sections of children's books.
Most good indie booksellers will happily supply photos of books by email if you ask. Very few websites have everything photographed as stock is individual and changes so fast.
The range of images at the top are of vintage children's books at March House Books from Barbara's range of gifts under £30. The Famous Five - Five Go Down to the Sea is from C L Hawley Books.