回复：Thank you again.

Read these links before the children travel to US:
https://help.cbp.gov/app/answers/detail/a_id/268/kw/minor%20child%20travel/session/L3RpbWUvMTM5MzQ0MjkyMS9zaWQveUdrcjFXTmw%3D
http://traveltips.usatoday.com/minor-child-identification-airline-travel-52409.html