This is false. The Colonies didn't have any common law that made children born into slavery as citizens. We know this from the charters of the original colonies, such as the Charter of New England that said, "Also, Wee do for Us, our Heires, and Successors, declare by these Presents, that all and every the Persons, beinge our Subjects, which shall goe and inhabitt within the said Collony and Plantation, and every of their Children and Posterity, which shall happen to be born within the Limitts thereof, shall have and enjoy all Liberties, and ffranchizes, and Immunities of free Denizens and naturall Subjects within any of our other Dominions, to all Intents and Purposes, as if they had been abidinge and born within this our Kingdome of England, or any other our Dominions." Simplified, this says every person, being a subject, and THEIR children born within the limits of the colony are natural subjects. They make an allowance for 'free Denizens,' which are legal aliens who are freemen. Part of being a subject (or citizen) means having your Liberty. Now how would that apply to the children of slaves??
Yes I know. It was a typo. I meant to say that children of slaves WERE NOT citizens under common law. Hence the need for the 14th Amendment to declare ALL PERSONS, not just free persons, born in the USA as citizens.
That's why the 14th Amendemnt was not redundant.