Over many years, evenings mainly, while my three sons were growing up (single parents don't get out much), I built the Project HappyChild website (non-profit) which reached 100 million visits on 3rd April 2011. The original reason for building the site was to highlight a range of UK-based charities helping children, the ones now shown in the Project HappyChild Directory.
Because of the timeframe within which it was built, the site includes a huge Pokémon area (still very popular) and a smaller one for Harry Potter, though it has been the tens of thousands of free worksheets (maths and languages, mainly) that have led to the huge visit levels (still ongoing). My personal thanks for volunteer help from across the world, particularly for the free dual-language worksheets (12 languages to English now, including French, Russian, Romanian, Polish, Arabic, Urdu etc.) which helped make all this possible.
UK visitors can support Project HappyChild by switching ISP to PlusNet and quoting happychild when you sign up (doesn't cost anything to "refer" Project HappyChild in this way but should give the site a small discount, for every month you stay with PlusNet). If you *are* able to help in this way, please do let me know by e-mail [penny2012 (at) happychild.org.uk] to make sure the site gets credited.