I'm pretty sure various charity coins have been tried/created before (though I can't recall the names of any). Whilst on the surface they may seem like a good and altruistic idea I don't think they'll be seen as anything other than another gimmick coin. I think it'd be better just setting up a charitable organization that accepts bitcoin to be honest.
I remember some alt that claimed its purpose was to provide clean water for third world countries but I guess it was a scam. Paying a charity money would have been more likely to help people.