You say you care about the Earth, and where it's headed for your children? You say you want to do *something* but you don't know where to start?
First, a piece of advice: don't go off half-cocked (shout out to NRA advocates!) without checking on what your purported charity does with their money, but check out charitynavigator.org.
Make sure you check out the organization that does the most with its resources, and don't put your hard-earned cash where it doesn't fit FOR YOU. This whole effort is designed to retain our precious resource, Mother Earth; think about where you get the most bang for your buck.