I just discovered that the British website of the campaigning organisation Stonewall has an excellent comprehensive list of books to recommend for all ages.
Type books into the search box of the home page.
http://www.stonewall.org.uk/what_we_do/at_school/3730.asp
Some of the books for younger children are not about sexuality as such but celebrate diversity.
And
This article lists a load of new books that I've not seen:
http://www.theguardian.com/childrens-books-site/2014/may/15/top-ten-lgbt-books-for-pre-teens-susie-day
