A group of teenagers singing at the Red Square (Красная площадь) in Moscow

This group of teens were singing just outside St Basil's Cathedral (Собор Покрова пресвятой Богородицы, что на Рву) at the Red Square. I'm not sure what song this is nor their purpose.

[yousefsaleh]

the song is probably yiddish and the teens are ultra orthodox jews