What a wonderful way of sharing your expertise!!!!!
Perhaps talking to the parents of children whose bikes could use some help about your willingness to work on their bikes for free and help the child learn about maintenance.....that could be a good way to start out and get parents and children talking about it.

My only experience is when I first moved here I joined a group of women who got non-working bikes from police auctions, rebuilt them and gave them to organizations who passed them on to children in need. It was a good experience all around!