If the father does not have full custody of the child, but is allowed visitation rights, he might be able to perform a DNA test on his own authority. He should consult his attorney to determine if this is possible. Here is the text that he will be required to sign on the behalf of the child at the appointment:

I authorize DNAForce, or its agents, suppliers or subcontractors to collect biological specimens and perform DNA testing with my specimen, or that of the minor or incapacitated individual(s) or individual for whom I have the legal responsibility named on this form.

If this test involves a person who is a minor or who is otherwise legally incapable of consenting or deceased, I attest that I have the legal authority to consent to testing and assume all legal responsibility. If this test involves a deceased person I further attest that I am the succession of this person.

The consenting adult is usually the person himself/herself if older than 18 years of age. However, for a minor, a person not legally responsible or a deceased person, it is their legal representative that must sign. I confirm that I have signed this form on the same day as the collection, that I have verified the information on this page and that it is true to the best of my knowledge.