Hello there,
If you’ll have plan to visit Vietnam, you can definitely travel with your two years old child during your family vacation with baby seat in the flight or car. However, there are some children policies which you should know:
Travel by Vietnam airline: infants from 14 days up to under 2 years of age in healthy condition shall be accepted only accompanied by their parent or authorized guardian. A 10% discount of the applicable adult fare is offered for infants under 2 years old and 75% for children from 2 to 12 years old. You can also use the baby basket service for your child, but only infants from 14 days up to 2 years old and whose weight doesn’t exceed 16 kg may use a bassinet. You should make prior request at least 3 days prior to estimate time of departure for domestic flights and 5 days for international flights.

Travel by car: If you book the tour of travel agent, you can ask them before. In other case, you should bring harness or small car sear for your child.
Hope this information is useful for you. Have a nice trip