I guess you really need a wide variety of books that are age appropriate for each age group. At the age of six they need books that are easy to read and have great illustrations. An 8 yr old could have books that have more words and less illustrations. A child of 10 usually like reading books, that have little or no illustrations, and are more beleiveable, like the Lion The Witch and The Wardrobe, Harry Potter, Saddle Club etc.
Some books I can think of that my children love and read time and time again would be Allison Lester an Australian Author who has a great story line and fantastic illustrations. Example of her books are Magic Beach, Yikes, Imagine and for the older children The Quicksand Pony.
Pamela Allen is another one that springs to mind again the illustrations are fantastic in her books as well.
Dr Suess books are always a good one to have on your shelves, Mem Fox, and exceptional author who captures the minds of the children. Shirley Barber has fairy books and for the young girl is another good one.
Now on a broad range of books, most libarys have Educational books, suchas childrens encyclopedias, dictionaries, childrens atlas's, books about emotions, where did I come from, science etc
Scholastic books have a huge variety of inexpensive books from childrens books to more educational books.
DK(DorlingKindersley) have again a large varitey of books.
They have a website. www.dk.com. But I think they are more costly.
Gould League books are educational books that are really good for the younger children, example would be australian guide to Whales and Dolphins, a guide to seashores etc.
I could go on forever, but I wont. Why not check out other libaries that are close to your area and ask them for some advise. I would even try a sending out a survey to the community and get their feedback on what their children like.
I feel you also would need to find out what religions, and cultures are in your area also, as you really want to touch on there upbringing and beleifs also.
Our Local libary that is run by our shire are usually volunteers, and every year they sell books so that they can update their stock. The volunteers are called friends of the Libary and if it wasnt for them, Our libary wouldnt be as good as it is.
Oh, also try not to just have books, try having videos or DVD's etc.
FYI, I have 3 children that love reading and they are 2,6,10 and I also do daycare. We also use our local library frequently as my books have been well used.
Hope this helps with some ideas and good luck . Its good to see people out there who are passionate about our community libraries.