I have no idea what these boys are practicing, but the 2 men on the right were the instructors.
The Temple was originally built in 1927-1929 under the name Temple du Souvenir Annamite (“Annamite Temple of remembrance”), primarily to honour the memory of Vietnamese soldiers who died while fighting in World War I. In 1955, the temple was re-dedicated to the memory of the founding Hung Dynasty of Vietnam.