File same forms for child as for you: I-130, I-485, I-765, I-131 , I-864 and do medicals ( I-693). There is no extra filing fee for the I-765/I-131 at this time and it is advantageous. You sign your name on all forms for child / applicant . Example Crabby Patti, mother
Use the same supporting documentation for both packets , make sure each packet has its own complete copy of documentation, then you keep a copy of each set as filed.
You seal each packet in its own envelope, then place both envelopes in one flat rate priority mail / medium box . On box write Attn Mailroom Supervisor: Family of Two DO NOT SEPARATE.