以我所知,你個兒子應該唔可以跟爸爸入籍,第一:Bb 出世時,爸爸只係綠卡,所以唔可以.第二: 就算爸爸入左籍before bb出世,爸爸入籍之後都要在美國連續住5年(我唔sure係要stay in USA for 5 年 or 入籍五年)以上先可以申請海外出生子女入籍,所以黎點對你黎講更唔成立. 以你情況,你個仔只可以跟你一齊入籍,如果你係結婚移民,住夠3年就可以申請入籍,個仔就自動入籍under 你申請.
你可以去uscis.gov website 睇睇,佢有清楚講明所以條例.
They make you write down the days that you are out of the country. So... If you arrive in April 2012 and leave dec 2012, then come back march 2013 that is 8 months stay during April 2012-2013 period.