The only way to prove the paternity of a child before is through blood testing. The blood type of the child should match the blood type of the father in order to say that the child is really of the father. But now, paternity testing has improved. We have now what is called private dna testing to prove the paternity of a child. But this is quite expensive. And I don’t think there is a need for this if you are faithfully married to a man.