Here's a UK website where you can vote for the best children's books. The numbers are still small but the selection of books is interesting:
http://www.devon.gov.uk/eal/dsls/cbc/childrens/cbclistmain.html


Here are the top 25 at today's date:
1. "Harry Potter and the Philosopher's Stone" by JK Rowling (26 votes)
2. "Bogwoppit" by Ursula Moray Williams (19 votes)
3. "The Wind in the Willows" by Kenneth Grahame (12 votes)
4. "The Hobbit: or there and back again" by JRR Tolkien (10 votes)
5. "Bottersnikes and Gumbles" by SA Wakefield (9 votes)
6. "A Wizard of Earthsea" by Ursula Le Guin (9 votes)
7. "Fattypuffs and Thinifers" by Andre Maurois (9 votes)
8. "The Lion, The Witch and The Wardrobe" by CS Lewis (9 votes)
9. "Jennings Goes to School" by Anthony Buckeridge (8 votes)
10. "The Silver Sword" by Ian Serraillier (8 votes)
11. "The BFG" by Roald Dahl (7 votes)
12. "Charlotte's Web" by EB White (7 votes)
13. "The Weirdstone of Brisingamen" by Alan Garner (7 votes)
14. "Harry Potter and the Chamber of Secrets" by JK Rowling (6 votes)
15. "Just William" by Richmal Crompton (6 votes)
16. "Swallows and Amazons" by Arthur Ransome (6 votes)
17. "Finn Family Moomintroll" by Tove Jansson (6 votes)
18. "Goodnight, Mr Tom" by Michele Magorian (5 votes)
19. "The Diary of a Killer Cat" by Anne Fine (5 votes)
20. "Nortern Lights: His Dark Materials 1" by Philip Pullman (5 votes)
21. "Harry Potter and the Prisoner of Azkaban" by JK Rowling (5 votes)
22. "The Demon Headmaster" by Gillian Cross (4 votes)
23. "The Story of Tracey Beaker" by Jacqueline Wilson (4 votes)
24. "Johnny and the Bomb" by Terry Pratchett (4 votes)
25. "Five on a Treasure Island" by Enid Blyton (4 votes)