Giving children money at New Year: from outside, Vietnam's lì xì and Japan's otoshidama (お年玉) look like one custom. Stand in the room while it happens and the manners diverge.
Where the names come from
Otoshidama did not begin as money. Its origin is toshidama (御歳魂) — the kagami-mochi rice cakes offered to the New Year deity, then taken down and shared out. Cash in an envelope became the common form only after the war, during the high-growth decades.
Lì xì is written with the characters for 利市, "profitable market", originally a shopkeeper's good-luck phrase, and cognate with Cantonese lai see. The red envelope belongs to that same family of customs.
Who receives it
Otoshidama is essentially something children receive. Adults rarely give it to other adults. It travels within the family, and is not usually extended to a colleague's children.
Lì xì reaches further. Children, of course — but Vietnamese people also give it to their elders. A working adult handing a red envelope to a grandparent or parent is entirely ordinary, because the gesture carries a wish for health and long life.
This difference produces misunderstandings at work. A Vietnamese employee offers a red envelope to a Japanese manager, who does not know how to respond. The intent is respect, and nothing is expected in return.
A different sense of amount
In Japan, preparing crisp new notes is considered courteous. The money goes into a pochibukuro, a small envelope, with the recipient's name on the front and the giver's on the back.
Vietnamese givers also prefer new notes, but what matters is the act of handing over the envelope, not the sum inside. Spreading small amounts across many envelopes suits the occasion better than concentrating them in one.
Do not open it there
Both cultures treat opening the envelope in front of the giver as poor manners. In Vietnam, counting the money in public is especially disliked.
If you are taking children to a Japanese home at New Year, this is the one rule worth teaching them beforehand.