No if a child was not born in legal marriage, a later marriage would not legitimize it. This was the case till a law was passed in the 20s or 30s which allowed children of parents who were not married when they were born, to be legitimized by their parents marrying later on. However this did not apply to peerages.. a child born to a peer, nad his ladyfrend, even if the peer married the mother later, woudl not be abel to inherit the peerage. Im not sure if that applied ot baronetcies