I agree with my colleague. For the 485, if a child can write his own name, I usually ask the child to sign. There are sections for the interpreter to sign in 485 if an applicant does not understand English.
Depends on the age of the child when it comes to I-485. As to the I-130, there is no place nor the need for the child or anyone else in his or her place to sign.
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A parents can sign on behalf of a child under 12.
Lynne R. Feldman, Attorney at Law
Concentrating in Immigration Law
2221 Camino Del Rio South, Suite 201
San Diego, CA 92108 | (619) 299-9600
Fax: (619) 923-3277
Former Adjunct Professor -- Immigration law
University of Illinois College of Law