I want my son to migrate here in USA from my approved petition when he is child

Is there a problem? As a naturalized US citizen, your child’s age is frozen as of the date that your petition is filed with USCIS. In other words, if your son is 20 and you filed the petition today, your son’s age remains under the age of 21 for purposes of his immigration case and he remains a child. I also note that this type of case typically takes about a year. Due to the limitations of the Lawyers.com Forums, Alan Lee & Arthur Lee, Esqs.’ (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.