When we went the tour guide that was with us for the 2 weeks took us to a local school so we bought pencils/books for them. Other than that there wasnt really that much opportunity to. unless you want to approach children in the street but most of them are likely to be in school so there arent that many about.
Whats best to do is buy lots of the hand made things there that the local village people make. These are very cheap but its helps the people to make a living and some of the things are very beautiful too. We ended up buying an extra bag to pack everything we bought.