In Texas if the father was to come forward, he would have to pay back child support from birth until death to KC.
Is the law the same in Florida?
No, from the Florida Statutes, Section 61.30:
In an initial determination of child support, whether in a paternity action, dissolution of marriage action, or petition for support during the marriage, the court has discretion to award child support retroactive to the date when the parents did not reside together in the same household with the child,
not to exceed a period of 24 months preceding the filing of the petition, regardless of whether that date precedes the filing of the petition. In determining the retroactive award in such cases, the court shall consider the following:
(a) The court shall apply the guidelines schedule in effect at the time of the hearing subject to the obligors demonstration of his or her actual income, as defined by subsection (2), during the retroactive period. Failure of the obligor to so demonstrate shall result in the court using the obligors income at the time of the hearing in computing child support for the retroactive period.
(b) All actual payments made by a parent to the other parent or the child or third parties for the benefit of the child throughout the proposed retroactive period.
(c) The court should consider an installment payment plan for the payment of retroactive child support.