This is such a great idea and such a wonderful organization, that you may have already heard of them. There mission is a pretty simple and straightforward one that you may have figured out from just their name. Little Dresses for Africa distributes dresses to schools, churches, and orphanages to Africa (47 countries there so far), and to girls in need in other countries like Haiti, Honduras, Mexico, Thailand, and even parts of the this country. They do also make pants for boys too.
Some folks sew. Some people help with things like shipping. Some donate money. The involvement though is huge with people participating here in the United States and Canada and also in other parts of the world. Some places even have sewing parties where many people come together at a time and produce multiple dresses to send in. Little Dresses for Africa is a Christian organization, but that doesn't restrict who can volunteer or donate funds.