這是USCIS的網頁上的。FYI
http://travel.state.gov/visa/temp/types/types_1267.html#2
--Exchange Visitor (J) Visas
--Spouses and Children
Spouses and/or children under the age of 21 who wish to accompany or join the principal exchange visitor (J) visa holder in the United States for the duration of his/her stay require exchange visitor visas (derivative J visas).