Vietnam is a not very large, but quite populated country in Southeast Asia, on the Indochina Peninsula. For many years it has been under Chinese influence. So a lot of Vietnamese traditions have gone from China. One of them is New Year celebration, which is usually has same date in Vietnam and China.
The difference between New Year in these countries is that in Vietnam New Year supersedes personal birthdays of people. This holiday, named Tet, considers to be everyone's birthday. On the first morning of Tet children become a year older and get red envelopes with presents.