回複：申請十年綠卡,一大一小,填幾張I-751表,交多少錢?謝謝了.

if jointly filed (with US spouse) and child got conditional GC through you together or following to join within 90 days, one form, one fee.

If not jointly, child got it later than 90 days or child now age over 21, child file his/her separate I751 and pay own fee.