The Mid-Autumn Festival is named "Têt Trung Thu" in Vietnamese. It's a traditional festival for the Vietnamese and also known as "Children's Day".
The meaning of Mid-Autumn Day is rather different to that in China, though the Vietnamese also celebrate it by eating mooncakes. In Vietnam the Mid-Autumn Festival is the happiest day for children, during which parents buy their children various kinds of lanterns and snacks.
As for origin of the Mid-Autumn Festival in Vietnam, it's totally different from the Chinese legend (Chang E Flying to the Moon)… Rice is harvested before the 15th of the eighth lunar month (mid-autumn) in Vietnam. Each household then offers sacrifices to the God of Earth. While occupied with harvesting parents have not so much time to take care of their children, therefore they make full use of the festival holiday to play with their children.
There are also various activities held to celebrate the Mid-Autumn Festival in Vietnam. The main activities include worshiping the God of Earth, and carrying carp-shaped lanterns.
Usually a worshiping platform is set up in the yard during Mid-Autumn night, on which mooncakes, fruits, and snacks are laid. Later family members sit together to eat the food while appreciating the moon.
The platform is not taken down until midnight, when the food is completely eaten up. Most families also set up a special platform for children, so that they can enjoy food anytime in the evening.
It's also a tradition for the Vietnamese to light lanterns during the Mid-Autumn night. A legend went that a carp spirit once killed many during Mid-Autumn night, so that no household dared go outside that night.
Later, a wise man thought of an idea: he made a carp-shaped lantern with a stick in its belly, and then advised people to walk at night with a carp lantern in hand. The carp spirit was terrified by the light from the carp-shaped lanterns, and dared not go out to kill at Mid-Autumn since then.
Now children hold various kinds of paper lanterns and play in the moonlight, while eating mooncakes during the evening of Mid-Autumn Day.
In addition, a variety of interesting literary and art activities are also held throughout Vietnam during the Mid-Autumn Festival, as well as offering sacrifices to dragons, dragon boat races, lion dances, and lantern fairs, adding much luster to the festival.