Every 28 years the sun returns to the exact position it occupied at the moment of its creation, at the beginning of the fourth day of creation. When that moment arrives, the "blessing of the sun" is recited.
The Rebbe taught that men, women, and children should be gathered together, especially since it is a year of hakel - a gathering of the Jewish people - to recite this blessing, thus increasing the glory of the King, as it is written, "In the multitude of the people, there is glory for the King.".
Furthermore, this event has a particular significance in the education of children (in age and knowledge) since it leads to the practical realization that the entire universe is constantly created and renewed by God.