Generally there is no statute of limitations on paternity. Most courts hold that once acknowledged, paternity exists and exists forever. However, there are some changes coming. By some estimates,about one third of today's children are fathered by a man other than the husband of the mother. Some courts are allowing men to disallow paternity by showing via genetic testing that they are not the father. The rule seems to be that if the father has objected before the child is 2 years old, the objection is valid.