Nov. 20, on this year a Wednesday, is Universal Children's Day, which was first established (or in international jargon, "proclaimed") by the United Nations in 1954. According to Wikipedia, the day "was established to encourage all countries to institute a day, firstly to promote mutual exchange and understanding among children and secondly to initiate action to benefit and promote the welfare of the world's children."
Though the United States does not observe the day annually at the national level, a tradition of observance predates the day's more famous cousins, Mother's Day and Father's Day. Many American church congregations have designated "Children's Days" at some point in the last 150 years. One of the first, in 1856, came when the Massachusetts Rev. Charles H. Leonard chose a June Sunday for the dedication of children to Christianity.
There are no strict guidelines for observation. The day's twin concepts promoting understanding and welfare include shedding light on many of the issues which afflict children around the world, including the important and damaging effects of chronic poverty and lack of education. For at least the last several years, the U.N. has been leading an initiative to ensure that all children are able to attend school.