I am not sure if it is a child born out of wedlock or a child from a previous marriage, but either way you would need to file a court action if the other parent is not willing to agree to the joint custody arrangement.
If it is a child born out of wedlock and the other parent would agree, then the two parents can sign a paternity affidavit and as part of that affidavit they can agree to a joint custody arrangement.
Answered on Jun 03rd, 2013 at 3:23 PM