Here is the situation: In order for the woman to request the fatherhood of the little kid there are many things that may fit into this: 1. The woman's blood type has to be OO. 2. The man's blood type has to be BO or BB. The child's blood type has to be AO or AA.
Here it is impossible for the man or the mother to have given the baby his/her A type so we may conclude that the man can't be the father. Another man with the A type must be the father.