How can my husband and I get custody of a child he had with another woman?

If you want this child regardless of whether he is your husband’s biological father, then a paternity petition must be filed asking to find that he is the legal father of this child. If he wants confirmation of being the father, he can request in the paternity petition for a DNA test. Once the paternity petition is filed he can obtain legal rights and/or responsibilities for this child, including time sharing.