Visa for children

Hi there,

- Can children get visas in the airport? (My husband and I are taking our three children with us this summer.)

- Can we get multiple entry visas in the airport?(We will be flying into Hanoi, traveling in Vietnam, then flying to Angkor Wat,  then back to Hanoi, then back to the US, so we will be entering Hanoi  two times.)

Thank you,

Susanna