'Child' in the Bible

Now what I mean [when I talk about children and their guardians] is this: as long as the heir is a child, he does not differ at all from a slave even though he is the [future owner and] master of all [the estate];

But the child of the slave woman was born according to the flesh and had an ordinary birth, while the son of the free woman was born in fulfillment of the promise.

But as at that time the child [of ordinary birth] born according to the flesh persecuted the son who was born according to [the promise and working of] the Spirit, so it is now also.