Originally Posted by After Shock Media

Quick search on Vietnam birthdays confirmed it.
Here is the quotes. "Vietnam - Everyones birthday is celebrated on new years day. Not only is Tet the beginning of a New Year, it is also everyone's birthday. The Vietnamese do not know or acknowledge the exact day they were born. A baby turns one on Tet no matter when he/she was born that year. Children say they were born in the year of the symbol of the lunar calendar for that year. On the first morning of Tet, adults congratulate children on becoming a year older by presenting them with red envelopes that contain "Lucky Money," or li xi. These envelopes are given to the children by parents, siblings, relatives and close friends."